If you are anxious about rust and what to do if it's present, you might consider taking the old windshield out first.
Use an exacto knife or box cutter to slit the old seal. Remove the aluminum trim on the front with a first cut and then take out the glass with another cut from the inside. These would be long cuts around the perimeter of the old seal.
If you have rust issues, you can address these before replacing the windshield without the installer being tied up. Remember, the seal seals the glass AND the frame. Unresolved rust on the frame will not allow a good seal.
Many glass installers will do the installation at your home. So, if you have rust or not, your installation work can be done on your own time frame.