What kind of bulb are you referring to exactly? Basking, MVB?
I've found regular basking bulbs to be fairly consistent from the get go, but it probably depends upon the bulb.
Our MVB took a full four days before the temps were steady, kept running hotter each day, so I had to adjust it quite a bit at first.
I'd just gauge them temps closely for several days when you install a new bulb, adjust as necessary.
Hope this helps!
Em