When to resend a patchset?

Hello Usually I was taking the approach of pinging a patch after 21 days of inactivity. This has worked ok in the past, but the last time I have done it I was told that the merge window was open and that nothing could be done at that time. Is there a written guideline to know when to resend/ping a patch? How can I figure out the current development status of the kernel? Anything better than the lwn? I dont want to wast useful maintainer time :) Thanks! -- Ricardo Ribalda