1 minute to turn on seems too long and 30 second turn-off seems too short.
I think these circuits usually look something like:
http://sound.westhost.com/project38.htm
Turn-on time for this circuit is dependent on how fast the sensing circuit can charge-up the capacitor that keeps the relay on. This should be pretty quick. Turn-off time should be based on the RC time constant of the charging cap and discharge resistor and I would be very surprised if it was intentionally less then 5 mins. Maybe charging cap is bad/leaky?