I've one block of 100 ORBs that has reached 951 confirmations and has weight=31
When will it be likely to begin stackin'?
Sometimes in only 3 or 4 days but it can take also much longer.
Big blocks will stake mostly faster (higher weight).
Some of my blocks haven't stake in months, others 3 times a month.
Just a matter of luck.
It's recommended to hold at least about 2000 ORB.
Here you can see a nice example of a wallet that holds less than 2200 ORB
and is having several stakes a week:http://cryptoguru.tk/Address/index.php?Currency=ORB&Address=oXpV4AUVzXFqExo7P2fCcSFibXFbucNigM