A moisture-cure adhesive
Automotive windshield urethane cures by reacting with water vapour in the air. That is why the wait is shorter on a humid 90°F afternoon and longer on a dry 45°F morning — there is more moisture available and the reaction runs faster.
Any technician who gives you the same number regardless of the weather is reciting a script rather than reading conditions.
What the bond is holding
Two things, both of which matter only in a crash. In a rollover, a properly bonded windshield contributes a substantial share of the roof's resistance to collapse. And on most vehicles the passenger airbag deploys upward into the windshield and uses it as a backstop to redirect toward the occupant.
An uncured bond fails at exactly the moment both of those matter. That is the reason for the wait — not the glass falling out on the freeway.
The first day
Leave a window cracked about an inch for the first 24 hours. Closing a door on a fully sealed cabin spikes the internal pressure and pushes outward against a bond that is still setting.
Leave the retention tape on for a day, close doors gently, skip the car wash for 48 hours, and avoid the roughest roads you know. A faint chemical smell for a day or two is the urethane curing and is normal.
Need this done rather than explained? There is no shop to drive to. We come to wherever your car already is — your driveway, your workplace car park, an apartment lot, or the side of the road it stopped on — anywhere in greater Sacramento, with no call-out fee and no mileage charge. Give us the year, make and model and you will have a firm price before the call ends.