actually got some items so far today...some after end of game...some after getting one shotted and leaving early very early, like in a minit and a half...so seems no 'time limit'...

Normally if there is a minimum time involved then it is specified in the event details.  I think I have had one within 5 mintues as well.  Unfortunately, the people who could confirm that for absolute certainty have finished for the weekend and it is not something I would use an out-of-hours contact for. 

From past events, its been 5 mins, even the 11-14PST item drops, I have noticed your luck is better at 5 min mark, or a little after the 5 min mark. I leave room at 5 mins. But the other day, during the 300% xp, the flag sunk before the 5 min mark for prem, and I still got an item.

Totally get it is not a complaint Star other than it would be nice to have more detail on these aspects to be 100% sure of what to expect. 

I have checked with the GMs and there is no linkage between the random drops in this event and the time spent in battle.

from what I have experienced, it seems the lower lvl you are as a bb the more drops you get. I suspect higher lvl people aren't going to be bestowed upon as much as lower lvls.