I don't exactly know what you mean by Region, so i just took the RegionID for you.
here you are:
USE SRO_VT_SHARD /* Decrease Monster Respawn Time By Midnight */
DECLARE @Rate smallint = 2 -- Rate to increase the respawn Time | 2 = 2x, 3 = 3x and so on
DECLARE @Region smallint = 28901 -- RegionID
UPDATE Tab_RefNest
SET dwDelayTimeMin = dwDelayTimeMin/@Rate, dwDelayTimeMax = dwDelayTimeMax/@Rate
WHERE nRegionDBID = @Region