Learn Dutch: We werken tot half zes. - We work until half past five.

This is one of the most important rules for telling time in Dutch! English looks backward at the hour that just passed ("half past five"). Dutch looks forward to the next hour. So, half zes literally means "halfway to six", which is 5:30.

What exactly does tot mean here?

tot translates to "until" or "up to". It marks the end of a time period. You will also see this word in common Dutch farewells like tot straks (see you later, literally "until later").

Why does the verb werken end in -en here?

Because the subject is plural. In Dutch, whenever the subject is a plural word like we (we), jullie (you all), or ze (they), the verb takes its plural form. This form is almost always exactly the same as the full dictionary word, which typically ends in -en.

Can I use wij instead of we in this sentence?

Yes, you can! we and wij both mean "we". we is the unstressed, everyday version that you will use most of the time. You would only use wij here if you wanted to put strong emphasis on the fact that we are the ones working (perhaps while someone else gets to rest).