Do a border hop. Don't plan to overstay. There's no reason to have an overstay stamp in your passport if you can avoid it.
Plus, if you get unlucky while on overstay, if you're stopped by a cop or immigration officer for a spot check (which happened to me at an airport - I was *not* on overstay so I was good), you can get not only fined, but banned from Thailand for five years - even if you have only one or two days overstay.
Poi Pet is regarded as the* worst possible place for border bounces.
The number of stories from Poi Pet of people getting rejected out of hand, including people who are blatantly genuine tourists with stays in multiple countries, is ridiculous.
Poi Pet is notorious for turning people away for *any* reason, and is best avoided.
The border guards seem to have a grift going with local Cambodian mafia. There are several reports of people walking away from the checkpoint, only for two Cambodians to appear out of nowhere, offering them the service of "helping" them, for a fee.
Each entry gets 60 days total; 30 days on entry, 30 day extension an option.
You're allowed two land entries per year, no limit on air entries.
So the answer to the question of how long you can stay here is this: You can do it until you can't.
The more visa-exempt stamps & extensions you have, the greater the likelihood that an immigration officer will look at your history, question you as to whether you're actually a tourist, and potentially deny you entry.
When that cutoff point comes is a matter of luck. Some get questioned after 1 or 2 stamps, others get to stay here for up to or even over a year simply by border-bouncing.
Land borders are the only entry points for which there is a legal, specified limit; no more than two in a calendar year.
This is a drastic change from when I first got here a decade ago, where there was basically no limit (being enforced). Back then, I used to run into people all the time who were here working illegally at village schools for pension top-ups, married to a local woman, and basically just going back again, again, and again.
I'd guess that it won't reopen at least until the regime in Naypyidaw falls.
Which, given the way the tatmadaw have been getting humiliated and hammered, time and time again, by the resistance of late, might not be too many months away.