If it's your first time 24-48hrs, if it's your 2nd 48-72hrs, if it's your third can last up to 2 weeks. If you got your 3rd strike and get banned after that, than they can take your key and or account with it.
[Causes]
Using any 3rd party program warden didn't like.
Messing with battle.net's servers in a way other than designed.
If this is caused by doing something that gave you R/D, than it will most likely only last 24-48hrs.
[CAUSES]
Changing characters too fast.
Creating/Joining games too fast.
Invalid logon due to invalid packet structure, AKA using a bot.
Sending invalid packets or too many packets too fast.
If I missed anything I am sure someone else will add to this list.
Time frames are based on an average scale. They may not be 100% accurate. They are rounded off in hours based on a full day.