How long for Mturk to decide?

The baord mentioned above is a great resource for learning who pays promptly. Amazon seems to take forever on their hits, but they almost always approve. I've had really great results with Geospacial and the product UPC people, too.

It all depends on the person that created the HIT. That person should go in and review the results then approve or decline the work, but if they don't and it just sits, the default for automatic approval is 30 days. The person that creates the HIT can change that if they want, when they create the HIT, but worst-case, it will be approved in 30 days if the requester doesn't manually approve it. Most of the bigger requesters (Geospatialvision, Amazon, Enrovia, etc.) are pretty good about approving the HITs within a week or so. There is a forum for Turkers at http://turkers.proboards80.com/ where people share their experiences if you're interested.

I guess they pay you when the hits are expired. Mine i took the hits that are near expiration and when they expired they paid me promptly.

It generally takes 7days to get approval from the requestor. But it depends. Some requestors post bulk jobs at a time. In that case they check after a certain point of time and take action on all their posted jobs at a time. And in some cases, requestors use to approve the jobs as soon as the workers work on it and submit the hit.