How long should it take to turn an apartment unit?

Assuming the apartment has been updated prior to the current tenant moving out it should take one week (max less than 2 weeks) to turn an apartment unit. When I say "turn" the degree I am am describing is new paint and clean.

You want a new tenant in there ASAP. If you let a unit go vacant for a month you'll be losing potential income and actual money when you have to pay the mortgage out of pocket for that month.

So 2 months prior to the lease expiring you should reach out to the tenant and confirm if they will be renewing their lease. If the tenant confirms that they will not be renewing their lease you should coordinate with your GC/repairman to start working on the turn the same day the tenant moves out. I would also coordinate with property manager to start screening candidates if possible (I am not sure if that is allowed, but I would check with my PM). Your goal is to get a qualified body in the unit ASAP paying you so you don't have to pay out of pocket.