The question of whether the parties can agree to extend time for compliance with a court order is an open one at the moment. See the discussion in the earlier posts on this issue. There was a short tweet earlier today by Charles Bagot of Hardwicke chambers.
“Put provision in Order permitting parties to agree 14 day extensions without an application; QB Master approved it; my #Mitchellsafetyvalve“
At present I think that this suggestion by Charles is the only safe option available to litigators. There is an ambiguity in the rules about whether CPR 2.11 overrides CPR 3.8. Further CPR 2.11 has a large caveat within the rule itself.
“Time limits may be varied by parties
Unless these Rules or a practice direction provide otherwise or the court orders otherwise, the time specified by a rule or by the court for a person to do any act may be varied by the written agreement of the parties.
(Rules 3.8 (sanctions have effect unless defaulting party obtains relief), 28.4 (variation of case management timetable – fast track) and 29.5 (variation of case management timetable – multi-track), provide for time limits that cannot be varied by agreement between the parties)”
It is not clear when, precisely, a court will find that the rules “provide otherwise”. An express provision in an order is, without doubt, a sensible course of action.