Getup early. Wherever you are, get a Grab car or a shared taxi or bus to South Bus Terminal in Bangkok. Go to platform number 10. Handover 110THB to the conductor and tell her Kanchanaburi. Bus starts exactly at 8.00 Am by their time. Get something to drink or eat while you're in the bus. It's going to be a 3 he journey in an AC bus. Don't hold your pee when you're in the bus. Do it before boarding the bus. Board the bus. Have a good sleep. We forget you are awake, you get to see the beautiful country side of Thailand.