I had a similar situation, It seems if you do the transfer electronically, same day its fine. I had to do 2 x 400k on 2 consecutive days as there was a 500k daily limit. Just provide books ,statements and letters from both banks to immigration
I went thru this when I renewed last year December 23 . Wanted to use a diffrent acc for the Visa money. Moved 400k one day 400 K next via transfer ( was 500 k limit to diff bank) more than 3 months beforebthe renewal. Got statements and letters from both banks to show had been over 400k for the year. Only problem was and was partly my fault. I didn't notice when I got the statements from SCB (the original bank) they only went back 3 months. So when I got to immigration I had to go to Jomtien SCB and get the full years worth . But apart from that no problem with it being spread between 2 banks
Air Asia has a one way to Phnom Phen for 1350 b one way. I had kinda the same thing going on, my return trip was 15 days after my 1 year extension was up for renewal, I don't think Cathay would have let me board without it
. Its just an hour drive from our place. And I am headed to there from Pattaya tommorow. Will go up Monday do the TM 30 in person and inquire about what all they need for the 1 year extension renewal in December . Thanks again