On a standard frame 10 speed it took me less than an hour to bolt the engine in the frame.
Another hour to bolt the sprocket to the spokes and true the sprocket by carefully and selectively tightening the bolts.
The chain tensioner took some time to think out how I wanted to place it, say another hour.
Cables, throttle and took some juggling. Tank bolted on pretty easy. another hour.
Pipe didn't fit exactly, so give it another hour to get right with some careful bending.
So 5 hours with a standard bike frame?
With a fat tube frame everything gets more difficult, add more time.
Start and run 32:1 oil right from the beginning to avoid plug fouling and muffler plugged.
Get out and ride!