It's a reasonable commute. The shuttles are timed to meet the trains. It looks like you're going to need Loop B, but just check to be sure:
http://transportation.westchestergov...opsSpr2015.pdf
The area is pretty pedestrian-unfriendly, so while the #3/12/13/62 and I-Bus stop near there, you probably won't be able to walk. So it's best to wait it out for the shuttle. The good thing is that there seems to be a shuttle meeting most trains, so that shouldn't be a problem.