So after I clean up the Gym, what time is Latisha supposed to come over to the apartment? I got her once, but since then she hasn't spawned.

She only comes once during the game. After you complete the game you can have her as much as you want, in fast sex. Also if you want to repeat the dance of the game , when you go to "stories click on the second tile and she will come around after you clean the gym. Have fun. I attached a pic of Latisha in "fast sex" to show the posibilities.

Maybe I didn't clarify; I've restarted the story, cleaned up the gym the first time and now I am waiting for Latisha to show up (I screwed up my first attempt), about what time is Latisha supposed to arrive at your apartment?

I'd guess around 20:00 or 21:00? You can try fast forwarding the time in the city map incrementally until she shows.

She will show up eventually later the same day during the night. Just wait a while in your appartment.

If you forget to check the locker and read Samantha's diary Latisha will not show. If you make it through the cleaning without checking out the diary and make it to your apartment, you will see the "thought cloud" that says, I should check her locker more. If you do check the locker more Latisha will come. The attached pic is from when I "forgot" to check the locker and followed the thought cloud . I went back to city view and to the gym and looked at the diary, then back to the apartment. Enjoy!

How did you get Latisha in that position at the gym?