I recently had to cancel a task on Seti. I don't monitor it very closely but I noticed on my statistics graph in Boinc manager that my Seti credits hadn't increased for a few days. I checked my tasks and found that Seti had one that had done over 23 hours of CPU time but was only at 30 odd percent and reckoned it needed another 54 hours to get to completion! With the share of my crunching time that Seti gets it didn't have a chance of doing that before it passed its deadline so I killed it. I haven't had any new tasks from Seti since I cancelled that monster one yesterday.
That sounds to be right. I've changed the option to not accept them.
I am planning to treat myself to a new computer after New Year. It'll be a quad of some sort so I might give those Astropulses a go again then and see how it handles them!