The US authorities don't have direct access to UK criminal records, so there are plenty of people on AB who will tell you that you can simply lie on the Visa Waiver form with no problems. Personally, I'd rather advise a 'better safe than sorry' policy.
Your conviction will never be 'spent' as far as the US authorities are concerned, so it's doubtful whether it would make much difference whether you applied for a visa now or later. The process takes about 5 months and is explained in my posts here:
http://www.theanswerbank.co.uk/Travel/Question 289769.html
Chris