Horn Circuit Timer

I installed Remote Keyless Entry on a 1994 Grand Am. It was a basic system. I added a couple relays and tied the parking lamps into the unlock circuit and the horn into the lock circuit. The parking lamps work fine, but the horn seems to blow for about two seconds. I would like to cut the horn time down to a chirp, if possible. I've read about 555 timers, but they seem a little involved.

I was wondering if I couldn't cut down the time the horn sounds by installing a capacitor and resistor on the coil side of relay #1. 

I've included my schematic and a capacitor schematic.

Will the capacitor and resistor work to cut down my time? I'm not sure of the size of the capacitor or resistor. Any ideas?

Thanks.

Thanks.

Is there some formula to arrive at these numbers? or is it practical working experience?

Thank you.

Hopefully, I'll be fixing this today.

All finished.

Installed a 10K ohm resistor and a 470uF capacitor. Horn chirp is perfect. Not too long or loud.

Thanks for the help.