Yes, you can request any length of extension, up to 4 years total time on your LPRP (or RRORP) orders. I know a guy who is requesting an 8 month extension to line him up for a summer move and the end of kids' school. The simple fact that it's not a nice, round year isn't going to cause them to deny it.

Turtle, they won't approve an extension for you, being a mobility guy. I just talked to the guys at HAF again this week, and there's still no chance of mobility guys getting extensions.