Learn Swedish: Vi är med och sorterar komposten klockan halv tre. - We are helping to sort the compost at half past two.

This is a structure called pseudo-coordination. When you use vara med (to participate) combined with och, the action verb that follows must match the tense of the first verb. Since är is in the present tense, sorterar must also be in the present tense. It literally means 'we are with and sort'.

Does vara med och always translate exactly to 'helping to'?

While 'helping to' is a great natural translation here, vara med och really emphasizes participation or being part of a group effort. It means 'taking part in' or 'joining in'. If you wanted to focus purely on the act of assisting rather than participating, you would use hjälper till att instead.

I always get Swedish time mixed up. Does halv tre mean 2:30 or 3:30?

It means 2:30. In Swedish, halv looks forward to the upcoming hour, so halv tre means 'halfway to three'. This is a common trap for English speakers, especially since 'half three' in British English means half past three (3:30).

Is it mandatory to include klockan before the time here?

No, it is not strictly mandatory. You could simply say komposten halv tre, which is very common in casual speech. However, including klockan (literally 'the clock') is the standard way to state a time of day in Swedish, acting much like 'at' or 'o'clock' does in English.