If we're going to go real RP time, by the time you would arrive the fight would probably be over, since it would take some hours to travel and the timeframe for most RP fights is at most thirty minutes to an hour.
That's pretty much the point. Unless the battle is supposed to be outstanding, then there was probably no reason for Kiri to assist Konoha at all (besides, the moment a key defender logs off the 'invasion' or whatever you choose to call it would be put essentially on halt if their presence is required, hence giving valuable time to any defenders not in the village to travel back). Though, travelling time between different villages would differ seeing as some are closer than others, with Kiri getting the worst of the lot having a sea to cross.
Well, Suna has a desert to cross, Kumo has a bunch of mountains with dizzying heights, Ame has a giant rain filled lake, Iwa has, like, canyons and deep ravines, and then you have that darn rebel Konoha that only has a forest to go through.
In retrospect, which would take longer would depend on mode of transportation. If everyone is flying, then I think you would get to Konoha faster from Kiri than from Kumo (just by scoping out the SL map).
If you have to walk or use a purely earth bound mount, then Kumo would definitely be faster, unless your mount is both a strong, fast, and well directioned swimmer.
*Plus, if the RP were to be stalled in the location, then arguably one still couldn't enter the fight till the appropriate time has happened in the fight, for things to catch up. By that's just over-complicating things, and it would be easier just to have limits on travel time.