Maybe a 555 is still the best way to go. There are many variants of the chip and it costs very little. If the task is a simple as described and production cost is to be low, it would be better. There are plenty of sample circuits. Just google 555 timer.
Moulding the case is indeed costly in smallish quantities.That chip marking I don't know, quite certainly not a 555 or it'd probably be marked with at least those numbers.
It's great for short intervals, but 3 hours is stretching it.