How many days after an AVF clots do you determine that attempting a declot procedure is no longer worthwhile?  

I don't really consider the number of days as much a factor as how many times the fistula has clotted in the last 6-12 months. If clotting is happening more often than every other month on average, then I think it is time to give up on the AV access. I am willing to tolerate 2 declot procedures ...