Is it the Bus station at Sukhumvit Rd near Pattaya Klang?

What times does it depart?

Walk up Pataya Klang cross Sukhumvit road and slightly to the right you will see a bus stop with several Thais hanging about waiting to catch a bus.

I usually get up there about 7AM, there are several buses heading to Rayong, I take anyone of those. From Rayong Bus Station I change and get one to Trat. You don't need a timetable to do this. When the buses are pulling up a young fellow will usually lean out the door, just yell out Rayong and he will take you if they are going that way.

There probably is a scheduled bus going to Trat but I have found my way of getting there easier and generally quite quick, good luck.