An hour's labour max. That's how long it took me; and that's with me manually jacking up each corner, removing the wheel, fitting the splash guard and then putting the wheel back on.
Sticking it on a garage ramp and taking off all four wheels at the same time should certainly reduce the amount of effort required!
Point to note: I had to shave a tiny bit off the rear inserts with a stanley knife to fit them in the OEM holes, because they are oversize as standard (this is mentioned in my previously linked RokBlokz YouTube video). I would maybe print off the installation instructions (
HERE) for the garage, or link them the video guidance (
HERE) for their assistance.