Try to respond to your survey invitations as soon as you can. Most market research studies are looking for a certain percentage of different demographic groups to complete their survey. That is why you sometimes may not qualify for a survey even though a survey is still open. If you are really late in responding, you may just get a message saying the study has been closed, which means they have recieved the required number of responses from all of the groups they were looking for.

The bottom line, the more a survey study pays out, the more likely it is to be completed quickly. Most of the really good offers fill up within a day or two, so be quick about it, and get the good paid survey offers!