Off topic: this was also my issue the past week as I’m on ED visa and Kasikorn particularly in Sukhumvit 33 which is considered a foreigner hub won’t allow to open a bank account unless you have a Work visa instead. Luckily, Krungthai Bank beside that allowed me to do so. Just need to have your passport and visa docs ready. You may want to try with them if Kasikorn won’t allow you.
You'll see the end date on the passport stamp; it's up to immigration whether they'll consider that as the same day or an overstay already. They'll surely let him/her know.