I think Thailand is in the time zone which is GMT plus 7 hours but for the next three days until we change our clocks, Mark will be 6 hours ahead of us.
As we embark on our geographical learning journey through Thailand, it is probably useful to set the scene with a map which sets the country in its context within SE Asia. As Mark has flown into Bangkok and will be cycling down the connecting isthmus towards Malaysia from there, he will only be travelling through the southern part of the country. As the map shows, most of the land area of Thailand is to the north of Bangkok. The isthmus which joins Malaysia to SE Asia is shared in its northern part by both Burma and Thailand. In fact, the first part of Leg 3 takes Mark to a point within 30km of the Burmese border before entering the southern part of Thailand which has a coast on the Indian Ocean (Andaman Sea) and the Gulf of Thailand.
The relief map shows that the Burmese/Thai border follows the mountain spine in the centre of the isthmus and as Mark's route will take him along the coastal lowlands to the east of that, there should be none of the arduous climbs he encountered in leg 2. There will, of course, be other difficulties such as much higher humidity and its attendant problems.