Assuming you're somewhere near the CQB limit, say 330fps, using 0.25s instead would probably drop you to around 300fps. Neither you or the people you are shooting at will notice the 30fps difference at CQB distances. The 0.25s will have lesser chance of BBs being blown off course by air gusts and the like.
I've played at indoor games with a TM MP7 shooting ~250fps with 0.20g. I used 0.25s, putting me at ~215-220fps. Still had no trouble shooting people at the other end of the arena.
You'll find this much more common in outdoor games. Very rarely will anyone be using 0.2 or 0.25g BBs for outdoor. Most people will have 0.28s or 0.3s, with others going even higher. Everyone adheres to the 400fps limit for outdoor, but that drops to ~320fps with 0.3s. Its still plenty to hit other people with. Plus the heavier BBs will be better in windy conditions or passing through brush and leaves
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)