That's easy: I don't spend any time building, just money buying!
However, that's changing now that I've been "retired" and have my life back.
My last kit has been in progress for the last fifteen (15) years… However, it's been a test bed for various techniques I've read in FSM or thought up out of my own fevered brain, so I'm not sure it counts. Actual "time on styrene" is probably about 100 hours, but I've built and painted a simple 1/72 scale kit in four.
To counter the endless agony of detailing and perfection that afflicts all modelers from time to time, my local modeling buddies (now all moved to other parts) used to have "slam build" sessions from time to time: You have one to four hours to completely build a kit, out of the box, and put one coat of paint on it. No finicking allowed. It was great therapy!