I wonder if the indicative present is good in the clause:
it is the requirement that, when John arrives, Mark be here
The answers are detailed but I wish to discuss the case “when becoming if” in order that I understand better:
When we wish say “if John arrives at the same time” I believe nothing changes.
it is the requirement that, if John arrives, Mark be here
When we wish to say “if John arrived yesterday”, then I do not see why it is not the past subjunctive. Past because it is on yesterday that we are focusing, subjunctive because it could happen or not (because of the if). So,
it is the requirement that, if John (had?) arrived, Mark be here
Is it with had or without ? what would be the difference ?
I changed the title.
NOTE: Since you have rewritten your question to examine a conditional construction with if instead of a time adverbial with when, I have banished my original answer to the end.
If I understand your new question correctly, you are asking what verb forms or constructions should be used with condition clauses (IF clauses) expressing either past or current eventualities when the consequence clause is a ‘mandative subjunctive’.
That is, you have a situation where an authority (let’s call him The Boss) gives an order to a subordinate (Mark) to be present under various circumstances involving John’s arrival.
The first thing we have to note is that a mandate, whether indicative or subjunctive, can only refer to an event which lies in the speaker’s future. The Boss may require Mark to be present in the future, but not in the past:
okBOSS: Be here this afternoon! … which might subsequently be reported as
okIt was required that Mark be present that afternoon.
But these are absurd:
∗ BOSS: Be here yesterday!
∗ It was required that Mark be present the previous day.
This is why a when clause with a mandative must employ a tense which expresses simultaneity with the mandated event. This sentence is absurd:
The Boss requirespresent that Mark be present when John arrivedpast yesterday.
This restricts the ability of mandative be to influence the other tenses in the sentence. The clause in which it falls is always actualized after the action of its head clause, regardless of what tense is employed in the head clause.
The second thing we have to note is that in Present-Day English, a condition (IF) clause which qualifies an imperative or mandate must be cast in the realis mode. It is true that in older English a condition clause in these situations often employed a ‘subjunctive’ form:
If music be the food of love, play on. —Shakespeare, Twelfth Night
If this be treason, make the most of it! —attributed to Patrick Henry
In those days, be was a true subjunctive, expressing subordination. But today, using such forms expresses irrealis mode: a tentative or counterfactual supposition—except in mandatives. A ‘mandative subjunctive’ is in all circumstances a realis expression; and we are not permitted to join an irrealis condition to a realis consequence.
Thus, The Boss may say this, with a realis condition:
okA1. I requirerealis that if John arrivesrealis you berealis here. which might subsequently be reported as
okA2. It was requiredrealis that if John arrivedrealisMark berealis there.
And he may say this, with an irrealis condition:
okA3. If John arrivedirrealis I wouldirrealis require that you berealis here. which might subsequently be reported as
okA4. If John hadirrealis arrived it would have beenirrealis required that Mark berealis there.
But he may not say this:
∗ B1. I requirerealis that if John arrivedirrealis you berealis here. so this is impossible, too:
∗ B2. It wasrealis required that if John hadirrealis arrived Mark berealis there.
Note the difference: In A3 and A4, the irrealis condition qualifies the action of mandating, which can be and is cast in the irrealis mode. But in B1 and B2, the irrealis condition qualifies the action mandated, which cannot be cast in the irrealis mode. Consequently, B1 and B2 are ungrammatical.
As you point in the comments, however, B1 and B2 are grammatical if their middle verbs do not bear an irrealis meaning—that is, if the mandate is based not on a counterfactual but on a still-undetermined prior arrival:
okB3. There are rumors that John arrived yesterday. I requirerealis that if John in fact arrivedrealis yesterday you berealis here tomorrow. which might subsequently be reported as
okB4. It wasrealis required that if John hadrealis in fact arrived Mark berealis there.
ANSWER TO THE ORIGINAL QUESTION:
It is the requirement that, when John arrives, Mark be here.
The when clause is not a relative clause but an ordinary adverbial time clause modifying the subordinate clause Mark BE here; and the that clause is not a relative clause but an ordinary nominal clause acting as the complement of requirement. So the matter of restrictiveness does not arise.
The when clause not only may, it should be expressed employing the indicative form. Adverbial clauses are governed by their head clauses only for tense, not for mood.
okIt will be a good thing if Mark is here when John arrives.
okIt would be a good thing if Mark were here when John arrives.
∗ It would be a good thing if were here when John arrive.
Note that although the tense in the adverbial clause is determined by the tense of its head clause, it is not necessarily expressed with the same form or construction as the head clause.
It was a good thing that Mark was here when John arrived.
It would have been a good thing if Mark had been here when John arrived.
The ‘present subjunctive’ form with commands and desires is usual in US speech and writing, and it is becoming more common than it used to be in Br speech and writing; but it is not obligatory in either: it may also be expressed with an ordinary indicative, or with should. But in all these cases the adverbial will take the same form.
It is the requirement that, when John arrives, Mark be here.
It is the requirement that, when John arrives, Mark is here.
It is the requirement that, when John arrives, Mark should be here.
∗ marks a usage as unacceptable