No. The T+60 rule is there so that what you just described cannot be used as a tactic. We are not going back to the days where a small # of a/c attack the target to say "see we made our attack", and then play "lets run the defenders out of fuel" games, or other gamey stuff. The strikes will be done within the T+60 time limit.
In real life the Luftwaffe had radar, you could not "hide" a 800 plane bomber stream. There was no "sneaky" way for the 8th AF or RAF Bomber Command to launch a major raid with escorting fighters, so I would not sweat it too much.
If the design needed an extension, thats the perogative of the designer, and it would be specifically written into the setup rules. In this case, there is no such provision. If you are finding the T+60 limit tight, I suggest not climbing to 25k, but perhaps 18-22K, or whatever works. Its up to you guys to decide the best way to conduct the raids, but dont climb up to 25k on a far target and then complain of time being short. You have flexibility.