we have done that journey twice before you get the bus from the bus station in mamaris to mugla and change there for bodrum the drivers on the buses will keep you right we usually go early on to make a good day out journey time approx 4hrs last bus back 8.30 but you can check at bus station

As Hagarg says it is quite a long trip and if it was me I'd stop overnight and go back the next day. An alternative route and maybe a good one for the return journey is a ferry from Bodrum to Datca and then the bus to Marmaris. I dont think it would be any shorter time wise and it will be a bit more expensive but it is a lovely journey. The ferries go about 9am and 5pm (double check this as sometimes they are half an hour later). They take about 90 minutes and get you to Kormen where there is a bus to take you 15 minutes to Datca. The buses to Marmaris go from the Pamukale office where they can drop you about every hour and there are plenty of cafes for you to wait in for your bus. The scenery as you go over the mountains on the bus is breath taking. Journey time Datca to Marmaris is just over an hour.

Hire a car and once you get out of Icmeler it should you less than 2 hours even if you don't know the road.

The roads have all been done now and nice and fast

John

It takes about 3 - 3½ hours by bus,