I look at it the same way I look at my firearms projects: It's gonna take a whole lot longer than estimated.
Case in point:
I started a "resto-mod" type rebuild of a beaten, battered, neglected, and eventually abandoned rifle. Easy. Quick flip.
Strip it, clean it, repair it, get it back to shootin' form, and upgrade a bit, in about three months.
Yea... that was Memorial Day, 2016.
I'm currently inletting the stocks - the blanks for which had to be custom cut, because I customized everything else on the rifle. For a professional, it would be about a 5-6 hour job (factoring for the custom changes).
Me? I'm about 22 hours in, and still not done. I figure the inletting and rough shaping will be about 30-32 hours, before I get to final shaping (an additional ~3-4 hours, including sanding). Finishing won't add many hours to the total, as it only takes 15-20 minutes to do the daily oil rubbing. But it still takes
time. I can only rub in another coat once per day, or more (minimum 24 hours between coats, often more). So, even though the finishing process only takes about 2-3 hours in all, that time is spread across about 10-14 days, when the project just has to sit.
By the time this "Quick Flip" is done, I'll have well in excess of 300 hours** in it. Hopefully, it'll be done a bit before Memorial Day 2020.
"Quick. Easy. I'll be done in three months..."

**(I'm probably short-changing myself there, all around. But I know for a fact that I never tracked CAD or paper sketch work. There was a LOT of time spent in CAD, designing some of the new, one-off parts that ended up on this rifle as replacements for the rusted garbage it came with.)