Depending on the project it can vary from 2 hours to a couple of days. Here is a list of the estimated time each service typically takes:
Mushroom vent ~2hr
Bathfan vent ~1hr
Turbine ~2hr
Soffit ~3hr+
Kitchen vent ~2hr
Dryer vent ~1hr
Ridge vent ~4-7hr
Gable vent ~2hr
Remove vent and patch roof ~3hr+