I found the time table online for the DMK to BKK shuttle. They say it can take between an hour and two hours. I'm curious how long it would take between early afternoon on a Friday from DMK to BKK? Trying to figure out which flight to book.

Early Friday afternoon is one of the most congested times of the week, especially as it gets closer to 4pm. Expect the trip to be close to 2 hours.

As an alternative (that is less traffic dependent) you can take the A1 bus from DMK to Mochit then the MRT to Petchaburi, then the Airport Link to BKK. Should take about 90 minutes. Total cost about 100 baht. Not great with heavy bags.