If you can prove the remitted money was from savings not earnings before the year you become a tax resident, those funds don't automatically give you a tax liability.
Ultimately they want you to prove financial self reliance. You absolutely need to have the full 500K in the bank. That said, if you're showing the last 6 months with 488K and then top it up to 500K a few weeks before applying, then you have pretty much shown stability. On the other hand if you only had 40K in the bank and topped it up to 500K a month or two ago then I'd be extremely careful which embassy I applied through.
If Vientiane you will be asked in for an interview appointment within a day of payment, expect 4-5 business days after payment or usually the same day after interview.