A 'dose' is considered O.5 mg, sprayed into each nostril, once or twice per hour. 5 doses per hour, and/or 40 doses per day, are considered the maximum safe usage limits. You can use the nasal spray for 3-6 months, but be sure to taper down before stopping use.
Source: Nicotine Polacrilex in Micromedex Healthcare Series, Vol 117. Thomson Micromedex 12/2002