When to interview?

Hello
My husband and I are going to be moving sometime next year, and I was wondering if anyone had a good idea about when to interview. The earliest I could start would be August, but I'm not sure when to apply for jobs. We don't have anything exact yet, but I will when I start interviewing. Is it better just to go interview and be able to start right away, or interview a month or two before my start day? Thanks for any help!
I'm also wondering this...because I heard it's not good to make employers wait but what if i am doing a program and can't start work till I"m done, how long is it reasonable to ask employers to wait before they pass u on and hire someone else, weeks or is a month too much?