The yeast gets to decide how long the fermentation takes, and whether or not it fully attenuates.
If you do all the things correctly, and pitch the yeast, it should be along the lines of previous comments. Let's say pitch the yeast and nothing happens for a few days... That can happen, you still may succeed, but it will be elongated.
There are many things that can inhibit fermentation, elongate the time it takes to complete, negatively impact full attenuation, or produce off flavors / aromas.
The yeast could be outside its best by date or expired. Yeast will generally degrade over time, liquid more quickly than dry yeast.
The cleaning and sanitizing regimen may have not been thorough enough.
A lot of us here use dry yeast exclusively, still more do a double pitch of dry yeast, do a yeast starter culture, harvest and reuse yeast on subsequent brew. The latter 3 can give you a stronger pitch that should take off faster, ferment stronger and finish to full attenuation sooner.
Ales generally take off about 12-18 hours after pitching. If there's nothing or really weak activity after 36 hours, be suspicious.
Lagers can take up to 2 days to start showing signs of fermentation. If nothing or really weak activity after 2 days or it's weak and stays really weak for a day or 2, a 2nd pitch may be in order.
You can monitor fermentation progress with a hydrometer; either an old school manual model, or a fancy electronic one like a Tilt. I like to use the tilt to keep an eye on things as they progress - or don't.
old school:
https://www.amazon.com/Brewers-Elit...8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1
New school:
https://tilthydrometer.com