And floss too. If it’s the evening, that’s a perfect time to do it. If it’s the morning, great time as well. Middle of the day? You’ve probably had food, brush them teeth. If you’ve recently (but not immediately after, wait a bit, drink some water) eaten, that’s a perfect time to brush. Especially if you’ve recently had something sugary (avoid sugary stuff, also like I said not too recently).
And if you can, and haven’t recently, see a dentist.
Your teeth are precious, and hard to replace. Lack of proper dental care can in many ways amount to a tax on the poor, where a lack of proper preventative care can turn mouths into an unaffordably fixable mess. Get people in your community to take care of their teeth too.
There’s really only a few situations where you shouldn’t be brushing your teeth right now: you vomited recently (brushing after vomiting can degrade the protective coating on your teeth), or you brushed recently.
Not having the equipment for it on you is only an excuse this once, carrying that stuff with you is a good idea. You eat and drink throughout the day, so you should brush and floss throughout the day. And who knows when you’ll need to be presentable? You don’t want to barrage your comrades, friends, partners, or “path to promotion” (your bosses) with bad breath.
Also, random fun fact, I pH tested a meal I have relatively frequently (took small bits of the meals components, in about the ratio the whole would have, then blended 'em up), and it came out as almost perfectly neutral (greens tend to be basic). I didn’t do that for the pH or anything, I was a lot more curious about what harmful materials it might contain. I had access to some relatively fancy unused lab equipment (or, more accurately, a friend did), so I figured I might as well use it.
Interestingly, while most brown rice had fairly high arsenic levels (as is expected), brown rice from this one local asian market was at white-rice levels. I didn’t ever end up doing anything meaningful with the data I collected (it’s just in a notebook I have), and it wasn’t really proper enough to be turned into a real study. Didn’t even ask the people at the asian market where they got their brown rice from (and then they shut down during the pandemic).