Is there a better time of year (for example, winter) to start immunotherapy or will similar results be achieved regardless of the time of year it is started?

Now. In general it is best to get started on immunotherapy as soon as possible to get the best result sooner. If you are currently having seasonal allergy symptoms now, getting started on immunotherapy now will get you on your way to significant symptom relief by the next spring season. Also from experience if you wait until your symptoms are not bothering you you may not be as diligent.