Good time for nasal irrigation:
Nasal irrigation washes out allergens and mucus, and also nasal sprays. So, before sprays and right before bedtime are good times for nasal irrigation.
http://www.natlallergy.com/cat/39/nasal-irrigation-sinus-irrigation-nasal-washing-sinus-rinsing.html nasal irrigation products.
Another device you may want to try is pulsating waterpik w nasal irrigator. Costs about $45.