So, of course, it depends on the volume of air in the oven (the size) and how big the oven burner is and what temperature you're pre-heating to. So I'll just hazard a guess of 15 to 20 minutes.

People who bake bread, often want a very consistent oven and will allow for a longer pre-heat.

As far as I'm aware of, gas ovens heat from the bottom only. The top broiler does not come on to help speed up the pre-heat.

It would be hard to say unless someone has a live one and can test it for you.

As to the mother of twins issue, we had one 18 mos and then the twins, all boys and a conventional gas oven and we made it through! In fact that time flew by!
I now have their babies,2 mos and 8 mos, a few days a week(kind of like old times) and have a fast preheating electric oven and comparing the two experiences, the preheat speed of the oven is the least of the issues! ;-))

My old electric ranges had a setting "preheat" - this turned on both the lower and the broiler element and they preheated pretty fast. The last electric I had, Thermador, didn't have a preheat setting and it took longer. My present all gas range doesn't have a preheat and I do not think I see any difference in the length of time from the Thermador.

I doubt there is much difference between them, certainly not enough to be concerned about.
My gas oven which is 4.2cuft takes 9 minutes to heat up to 350 degrees.

There are differences in pre-heat times among various ovens and types of ovens that have been discussed here previously.

Less-discussed is the fact that just because an oven's thermostat indicates the selected temperature has been achieved, it may not be fact. This is pretty easily researched via placing thermometers at various places in the oven cavity. The location of the oven's own thermostat usually shows up-to-temp. indication earlier than other oven locations.

And then there's the stabilization thing so dear to the hearts of bakers. Like everyone else, bakers want to depend upon the temperature selected but they also want a temperature-stabilized cavity. Stabilization-at-temperature requires some dwell time beyond just up-to-temp indication regardless of type or brand. Basically, they want to wait until the walls and racks are up to heat and stabilized at the selected temperature as well as just the air inside. For myself, using a GE Profile electric oven, I generally plan on waiting 10-15 minutes after indication of selected temperature before I put my loaves of bread in. Other brands and types would probably be different but the principal is the same for all.