My friend attempted to drop off his 2 year old son to his ex-girlfriend's home today, as previously agreed. They share joint custody but she is the custodial parent. She was not home at the agreed upon time and has not responded to his attempts to contact her. After how long might he have grounds to claim child abandonment? If he cannot, is this act grounds for him to attempt to seek sole custody or any other recourse? Thank you.

The first and foremost concern should be for the mothers safety at this point. Not how to mess her over. Then once you have found that out you can determine what steps to take from there. Until you know that she isn't dead its best to take it a little easier.

CalifDad is right. In all states, there would be at least a 6 month period of no contact before he can file for a change of custody. BTW if you read the sticky note at the top of this forum you would have known that he can't "file" for abandonment. He must file for a change of the custody order! He can use abandonment as a grounds.