I second the idea of the trainer if you need to work around work. And you should be able to pick one up for cheaper now because bike shops are trying to get rid of them for spring.

I don't have specific advice (intervals alternated with time in saddle or distance trainer sessions/rides maybe?), but don't dive in head first because you're trying to make up the time. You'll be more likely to injure yourself or burn yourself out that way. Ease into it.

Good luck!