Does anything apart from gravity and relative velocity affect time? I have been learning about time and the different dilation effects of gravity and relative velocity. I was wondering, are there any other factors that can affect time?
 A: As far as I know, the answer is no.
The time dilatation effects of special and general relativity are associated to the transformations between different frames of references.
There is no a-priori time: each observer in his frame of reference measures his own time, and it may happen that observers in different frames measure a different time length between the same two events turns different. 
This is what we mean with time dilatation.
However, it is just an effect resulting from the fact that different observers belong to different frame of references. That is relativity.
Gravity can be seen in a geometrical way in GR just thinking at is as the curvature of spacetime. So you could say that gravity as a force "does not exist" and rather what we call gravity is just a feature of spacetime. It is encoded in the spacetime structure, and therefore creates "time dilatations", which are again effects perceived by different observers sitting in a frame of reference in spacetime.
The other forces we know of do not admit such a geometrical interpretation. Rather the "live on" the spacetime (hope this makes sense). They can not be seen as part of spacetime itself and therefore do not produce time dilatation or length contraction.
