All Abra transactions are verified by the blockchain -- this is how we can ensure the money you're sending is yours to send. It's one of the ways we prevent fraud in the system.
Bitcoin and Litecoin:
It can take from 10 minutes to 4-6 hours for transactions to be confirmed on the blockchain, depending on that specific blockchain (Bitcoin blockchain or Litecoin blockchain depending on which cryptocurrency you're sending) congestion at the time you initiate your transaction. Until Abra gets confirmation that the transaction is a valid and unique one, you won't be able to send or withdraw the funds in your Abra wallet.
Bitcoin Cash ABC:
For all BCHABC transactions, Abra will now require 15 confirmations before transactions are confirmed and reflect within your Abra wallet. These additional confirmations are required because BCH forked and the hash rate was reduced.
Due to this, BCH transactions are now going to be delayed for your own protection.