Actually the "lifetime" of FPLs in IFPS is EOBT+Total EET+3 hours.
E.g. a flight from Barcelona to Manchester, with a EOBT at 10:00, flight time 02:01, will close in IFPS at 15:01.
That means that technically the AO can send a DLA/CHG well past the EOBT, which will be accepted and distributed.
So, in principle ATC systems must be able to accept updates well past the 30 min nr.
Still, as mentioned before ,AO's have to update their EOBT if delaying more than 15 min.
Failure to do so, in areas where Flight Activation Monitoring is enabled, will entail an FLS at EOBT+30 min if nor reported airborne.
rgds