That’s ridiculous. If you want to make your own chumra you’re entitled, but you have no right to demand that others follow it. Five hours is enough buffer time to allow for all reasonable delays; more than that is an extraordinary event that one is not required to allow for, and is certainly not required to lose a day’s work for.
There is no difference between a long- and a short-haul flight. A 15-hour flight is no more subject to delays than a 45-minute one. On the contrary, the longer the flight the more chance there is to make up time lost to delays.