Add up your wee bits at a time, surprising how much it adds up to.

Ive done two so far. First one, electric glider took about 3 hrs in total but I made it longer by changing the servo setup from a single aileron to two servos. I had no engine or fuel tank to mount in it though. It couldve been done in half an hour out of the box at the field if need be, everything was done right down to battery pack holding straps and ESC soldered on etc.
Second one was a Blackhorse CAP232, Id guess at about 8hrs over a couple of nights to complete. It was my first glo ARF, so mounting an engine and tank etc was new to me. If I take into account curing time for the epoxy to join wings etc itd be more like 30+ hrs total. I like to let 30min epoxy cure for at least 24 hrs before subjecting it to load.
I once bought a glider that said ARF on the box but it was more like Almost ready for you to do all the tricky fiddly wing joining, mounting blocks, tap threads sand wings, cover or paint etc. etc. Everything except lay up the glass fuse, sheet the wing cores and cut-out the tail surfaces had to be done. I WAS SPEWING considering its price tag compared to the Blackhorse CAP or E-Glider. It was 1/3 MORE expensive but is a fantastically awesome model now its finished.