1. Urethane is the black adhesive which bonds the windshield to the vehicle.
2. In case of an accident, the windshield could pop out if it has not met the safe drive away time period.
3. I suggest to always ask the glass company and the installer what Brand and Type of Urethane they will be using at the time of installation.  Also ask them if they are certified in the urethane that they are using for replacing your glass.

I always like to do my homework before I make a buying decision so I have compiled the most commonly used Urethane Manufacturers to help you do the same.  What you should be looking for is the Manufacturers and the type of Urethane to be used.  Also look at their safe drive away charts.