Acceledent treatment. My orthodontist told me to use it twice a day once in the morning and once in the evening. Is this okay?

Acceledent is recommended to be used 20 minutes a day only. using it more  than that not only is not recommended it won't make your treatment time any faster.

While using Acceledent more than once a day is beneficial for reducing orthodontic discomfort, it will likely do nothing to further accelerate the rate of treatment. There are currently no studies evaluating this scenario in orthodontics, but we know from the orthopedic literature that maximum results come from 20 minutes a day.

It is recommended to use the Acceledent for a total of 20 min a day. 10 and 10 is perfectly ok. Best of Luck! 

I recommend this to my patients everyday and do it myself for my own Invisalign plus Acceledent treatment. It is a great suggestion. 

Acceledent is a safe, gentle, and effective medical device that can both reduce the time and increase the comfort of your orthodontic treatment. The maximum effective use of the "soft pulse" device over your existing orthodontic appliances (braces or aligner trays) is 20 minutes per day. You can wear the small device, which has a soft bite plate connected to a base that is slightly larger than a Bluetooth ear device, at two separate times (10 minutes each) or for 20 minutes at one time per day. The device contains a "chip" which can be downloaded to monitor your compliance as well. It is truly an ingenious technology, that speeds up the essential bone remodeling that enables teeth to safely move which is the cornerstone of effective orthodontic treatment.

Acceledent is a fine tool to reduce the treatment time.  for all types of orthodontic appliances.  That being said, I believe your orthodontist recommendations are sound.