Ya, thats true, no precision timing. I learnt it the hard way. I was using a 555 for the detonator of my fuel air explosive. Its got 5 liter of petrol and a 50g ANAL charge in the middle. I set it to 15 min,(cause I thought these things are nice and accurate and stuff.) and ran for cover. I waited and waited until like 20 minute have past. Then My friend and I thought something is wrong so we went to check, and when we were like 10m from that thing you just see a huge fire ball, as bright as the sun, we got thrown back a few meters and burnt our eyebrows. Haha. So listen to Sceadwian, don't use it for precision timing.