In my Return to the Tomb of Horrors campaign, we had this problem (not with delayed blast fireballs, but with the gloves). There was a 5+ page long thread about it that I'd love to show you, except the stinkin' search feature doesn't work.
Basically it was decided that being able to extend spells indefinitely is out of balance for a 2200 gp item. However, that being said, I did not stop doing it in my current campaign. both the PCs and the NPCs have used the tactic for too long to warrant changing it mid-game. However, for my next campaign, I'll be ruling that spells continue to function while within a glove.
If you've yet to have any issues poop up in your campaign with gloves of storing, I' go ahead and rule this way ahead of time to avoid them.
Of course, in my campaign the party has been fighting a Necromancer for quite some time. If she survives the next encounter, she'll have to go get Delayed blast Fireball so she can booby-trap her gloves.

The party frequently uses energy immunity (fire) though, so it isn't a viable combat tactic for her.