My water heater has a 16 sec delay on start. I toggle the rocker switch, the switch lights up along with the fault switch next to it. I count to 16 and the water heater ignites. Says it is supposed to do that in the manual. I am not near the trailer right now to check what brand I have. Check your manual and see if it is normal to have the delay.
We bought our trailer used and our first outing was one of learning about the trailer. The water heater ignited immediately on gas (no delay) and I starting troubleshooting a problem when at home it would not start immediately, but rather turn on fault. It took some studying (and help on this forum) to get the information that the initial behavior was the problem and the delay was the correct behavior.
If I recall, the manual said something about the delay being for "purge". Perhaps yours is not purging and there is more gas there than expected?? Just guessing.