Depends on the ammo load I should think. And where you hit it with what. Most of the Syrian tanks we saw after were still sitting where they were hit years later...some are still there.
Here's an example. Hard to say what the hit really was done by, looks like editing of the beginning. This is a typical tank cooking though... There's lots to examine.
A Tank Syrian Arab Army burn after attack wit RPG by FSA / Syrian Terrorist - YouTube
That took lots of time and usually the guys would be standing there coaching you, because your keys were sitting on the seat inside...right where you left them.