Hello, I am a US citizen staying in bangkok. I have been looking for work here for about a month. I was wondering how long it takes to change visa to non immigrant and apply for a work permit once I find a willing employer? Thank you in advance for any help.

No delay once the paperwork is in order.

You can apply for a work permit with a tourist visa. Then with a letter of approval for the application you can get a non-b visa from a nearby embassy or consulate.

After you have the non-b visa the work permit will be issued.

I would guess the minimum time to this would be about 3 weeks.

Nearby consulate or embassy in Thailand? or i have to leave Thailand to a surrounding country? it says online its best to do it in your home country but is it required? Thank you

You do no need to do it in your home country. Non-b visas are done all the time at the nearby embassies and consulates.

Perhaps you were reading about getting a multiple entry non-b visa for business purposes.

Thai consulates tend to be outside of Thailand.