@Je***
yes you can make that flight back, I have done it several times. It's essential if you want to make that flight back that you get an early number the first day because they are given back the next day in the same order.
I usually then ask around at the consulate if anyone is going back to Udon Thani and try to arrange sharing a taxi to the border at least. If you have four people taxi all the way to Udon (arrange at the border) is as cheap as the minibus- and sometimes on the way back it seems hard to get minibus from the border to Udon. And you don't have much margin- so have usually got a taxi on the way back, sharing with other people I met either at the consulate or at the border.