1. Cancellation is done on same day of request.
2. Exit permit is issued with the cancellation of visa also on same day. (The exit permit has a limit of 7 days to go out, if the period is exceeded, new exit permit can be obtained for next 7 days.
3. You can come again to Qatar on Visit/Business/Tourist Visa, but there will not be any opportunity of working only if you can obtain NOC from previous employer.

hope information is useful for you....

regards,

Rashid