Response: I don't know if it is safe with sleep apnea, but regarding when it is meant to be taken...it depends upon the specific situation of the patient and judgment of the prescribing physician.  Anxiety sufferers may take Clonazepam at any time during the day as an "as needed" medication or as a maintenance treatment.  For others, it is used as a sleep aid.  For example, some anti-depressants are engergizing (Effexor for example) which make it difficult for those taking it to sleep.  Low doses of Clonazepam may be prescribed in that situation to be taken in the evening.