I’ve just finished replacing the groupset on the wife’s winter bike. It took just under an hour to strip the old stuff off, another hour to thoroughly clean the stripped frame and then a total of 3-4 hours to rebuild including bar tape and mudguards (rim brakes though).
Issues were that wiggle didn’t seem to think that a 105 groupset should include a front mech, so I had to wait for them to send one, I had to pop out for outer cables as I didn’t have any I could use, the rear calliper didn’t fit the frame so I needed to bodge it a bit with part of the old brake and then I had to actually read the instructions for the new 105 front mech as things seem to have changed since my day – sticky bits for the frame, random, adjustment screws and a strange plastic tool for seeing which way the cable should go?!?
Anyway OP, music on, tea/beer to hand and just enjoy the process. Think how much better will you understand your bike now.