I won Judgement but Defendant wants to make monthly payments

I recently took a defendent to small claims court in the state of Washington and won judgement against the defendent. The defendent has sent me a letter requesting he be able to repay on a monthly basis over a two year period.

I doubt I could collect the entire amount at once from the defendant. Should I refuse to accept monthly payments and demand full payment even if would require that I certify the judgment and start the wage garnishment process. If I allow the defendent to make monthly payments should I still certify the judgement or wait to see if he doesn't make monthly payments?

I know in the state of Washington you have to wait 30 days before you can certify the judgement but are you required to certify a judgement within a certain time period? (e.g. within 1 year)

Thanks in advance for your advice.

See http://www.worldlawdirect.com/article/935 -- Collecting on a court judgment.