Should you take pristiq (desvenlafaxine) at night or in the morning?

It depends. The medication is generally written for daily use. Whether you take it in the morning afternoon or evening depends upon your preference. If it makes you sleepy you may want to take at night, if it seems to bother your sleep you may want to take it in the morning. It is however best to take it at the same time each day. That way you are less likely to forget to take the medication.
Pristiq (desvenlafaxine) Since drowsiness is a reported side-effect, it is advised to take in the evening, once daily.