The GWP is computed for a period of 100 years to account for the various half-lives. The 25x figure is normalized over a 100 year period.
Over a 20 year period, it is about 85x more harmful
So methane control is a significant handle to control global warming. It is not a solution but it will buy time if we globally "burn" methane to COP2. See BlueDotChange.org.
Doesn't methane eventually break down into carbon dioxide? If it does then it's much worse than just being co2 in the first place.