Beseler lamp delay
I bought (many years ago) a brand new Beseler Universal colorhead for my 4X5 enlarger. From the beginning, I had (and still have) intermittent occurrences of the delay you talk about. Actually, the solution is very simple. I discovered through trial and error that it happened more frequently if the interval between times that I turned the lamp on was longer. For example, if I focused my image with the lamp on, and then allowed more than one or two minutes to elapse before putting the paper in the easel and making the exposure, the delay was more likely to occur. However, if I went straight from focusing/composing to loading the paper and exposing, with no more than 30 sec. to a minute in between exposures, it almost never occurs. Try experimenting a bit to see if this helps your problem as well.
Originally Posted by Phoebe
The other thing I noticed over the years was that even in cases where I got the delay, I couldn't tell any visible difference in the print. So I also wonder whether the light stays on after the timer counts down for the same length of time as the starting delay.