As we see in the MLP universe the ponies themselves have control over when seasons change (via Winter Wrap Up, Fall Run, etc) so there is no natural reason for seasons to change. Is there any indication that a pony year progresses in the same way that our year does? Could you artificially speed up seasons?
One of two things is likely. Either seasons are made to progress at roughly the same rate as they do on Earth, or they run at a faster than usual rate. Arguably the latter is more true, given the short amount of time between Winter Wrap-Up (clearing out the snow and most clouds, waking up hibernating animals, managing bird migration, etc.) and the Running of the Leaves (marathon race with the purpose of shaking leaves off of autumn trees).
The above is a bit of conjecture though, since the topic of seasons is really not mentioned much aside from in the episodes Winter Wrap-Up and Fall Weather Friends.