The meeroos go to sleep when the Sim time is night and wake up when the sim time is day. If your sim is set to always night this will effect there sleeping habits.

This Is NOT effected by the Client Day/Night override.
It is effected through the Sim settings itself. If a Sim Owner sets the sim to ALWAYS NIGHT through the Sim Admin options then the meeroo will always sleep.

If you rent land from a sim and every time you port there its night time and you never see your meeroos awake, you may want to contact the sim owner or admin to request they set the day/night cycles to normal SL cycles.