That’s entirely dependent on the embassy or consulate you use.
Typical turn around times for London are about 3-5 days. US consulates are about a week. France and Germany are about 3 years (well not exactly but it feels that long). Other embassies could be different.
There won’t be a problem about not having an exit stamp as they are aware of the “automatic gate” system.
No one can say if you’d have an issue re-entering Thailand as that’s up to the individual immigration officer but it’s highly unlikely that they’d have any issue with those dates.
They’re on the look out for repeat entries after an extension which could mean you’re trying to stay in Thailand without a correct visa.