There are other options besides candles, for example a ceramic tea light holder where you simply add fragrance oil or essential oil diluted with water. There are longer burn tea lights available that I think last 4 hours, tea lights are as cheap as chips too. Example:
https://www.ebay.co.uk/itm/194757044816?hash=item2d586caa50:g:oRsAAOSwT-Vky6wM
Another option is reed diffusers either ready made or you can make your own which is what I do. Again, another cheap option where you could have several in the room.
An ultrasonic diffuser could be a good choice, fill with either fragrance or essential oil and add water then simply plug in. These can last up to 8 hours, depending on capacity. Huge selection on the mighty ‘A’.