The table you're looking for is spawn2, fields are respawntime and variance. Values are in seconds.
Code:
UPDATE spawn2 SET respawntime = respawntime/2, variance = variance/2 WHERE respawntime > 1200
That would cut spawn times in half globally unless they are less than 20 minutes. For most purposes you probably don't want a spawn time to fall under 10 minutes.
In that past I've ran simple queries to cap spawn times, like
Code:
UPDATE spawn2 SET respawntime = 14400, variance = 2400 WHERE respawntime > 14400
This would effectively set a max spawn time of 4 hours.
Of course, using pop lyrics in your sig makes me want to suggest DROP TABLE spawn2.