Can I obtain a tourist visa in Vientiane and switch to a retirement visa afterward?

It used to be 24 hours officially. But hey its Thailand

You should take time to learn what are the existing visas. Then going to Vientiane or anywhere in Laos is a good idea. You can come back the same day with a visa exemption only, provided that the immigration thinks you can still have one. For any kind of visa, you have to apply online in Laos or any other country. It takes at least 2-3 working days for a tourist visa and more time, sometimes much more time, for other categories of visa.

No. If you want to apply for a tourist visa you have to travel to Laos, apply for the visa using the evisa system, visit the consulate and pay for the visa then wait for it to be issued before returning to Thailand. If what you want is a visa exempt entry and your passport entitles you to one then you can cross the border and return to get the entry stamp. BUT you are currently on an extension of stay based on working inside Thailand so before doing this you should cancel your work permit and the extension of stay prior to travelling to Laos. I'm not really understanding why you are so desperate to do this? Is your current extension of stay due to end imminently and before you are able to cancel your work permit? Or is there something else driving this?

Colin Dorman . . if you already have a Thai bank account in your sole name with a minimum of 800,000 THB already sitting in it, and a rental contract, you can theoretically do the "change of visa type" from a visa-exempt entry to an initial 90-days Non-Imm-O retirement visa. . . . in case you got none of that, you need to expect to pay an agent up from 60,000 THB to 90,000 THB to get around the existing law

You apply online it’ll take at least a few days and you should apply for a non-o and extend that for a year

For over 50 years of age 100% easier & cheaper to apply for a Suitable retirement Visa from your home country

When you are ready to come - Apply for a Non-O 90 day Visa from the Thai Embassy in your home country about 30 days before departure.

When applying online you will need to show the required funds in any bank account , some personal details & Flight details & proof of first nights accommodation .

Once approved & arrive in Thailand you have 90 days to organise for the 12 month extension

No.1 requirement is

You need to set up a Thai bank account & deposit 800K Baht for at least 60 days to satisfy the extension

Go to the bank of choice & ask them what they require to open a bank account

You can also come to Thailand on a tourist Visa & get it converted to a Non-O retirement Visa for a much higher cost

In short - No

You could get it all done in Thailand through an agent

If you are prepared to pay the $$$