Sealcoating can last up to 3 years but you may need to re-seal more often. Generally, it's a year.  The variable that determines how often to seal coat is if there is a lot of heavy traffic on the surface, especially from heavy vehicles, chains on tires, chemical spills, and harsh winter temperatures. 

Surface deterioration displaying minor cracks and discoloration from black to grey hints that it’s time for maintenance.

Weather determines when you should sealcoat. The best time to do the task is when it is warm because you need plenty of sunlight to quicken the drying process. Be careful during the rainy season as the rainwater will extend the drying time. Make sure to listen to the local weather forecast.

Make sure that there is no water on the surface and that your sprinklers are turned off 24 hours before the sealcoating process.

 If there is grass along the area, do not fertilize it for a week before sealcoating. The work area should be cleared of all vehicles, equipment, and any other obstacles.

The time it takes for the sealer to dry depends on the humidity, temperature, and sunlight. 

Stay off the pavement for at least a day if there is enough sunlight.  Usually after this time, you may walk and drive on the surface. 

Yes, this is expected when a new sealer has been applied. The marks will go away within the first month or after the sealer has completely dried.