Exactly. The fire should kill most of the weed seeds then the tilling will get the ash mixed in well for the nutrients and break up any roots that might still be alive.

Till it now, tilling later will bring up more weed seeds. Till and water now. Then pull a heavy platic silage tarp or pond liner over the area. Weight down the tarp so it has contact with soil and it nice and tight. Leave it like that until mid spring when all the seeds have germinated and then been killed by being smothered and decomposed under the tarp.