Comment by gary_0
Yes, a simple purpose-made chip designed to be used in safety-critical situations, with high tolerances for voltage etc, would probably be better. Although one thing the 555 design has going for it is that a seasoned EE could take one look at the physical circuit and know exactly what it does.
But I would never trust anything that ran software for something like this.
It depends on the system's potential failure modes and what's required by your safety standard, not on one engineer's opinion of what's "best".