1. As long as you like... There are no limits in the Bitcoin protocol.
2. Your transaction can only be mined if you broadcast it to the network with adequate fees. When you are ready, you send it.
3. If you haven't broadcast it yet, only the copies you have made exist, and are not yet immutable. Once you have broadcast the transaction, it instantly exists on every node in the network, and once confirmed exists in every copy of the full blockchain. Your local copies also still exist and are what you should draw from in future. The copies in the ledger are there so that you can a) prove the data hasn't changed and b) get it back again if you ever lose your copy.
1. As long as you like... There are no limits in the Bitcoin protocol.
2. Your transaction can only be mined if you broadcast it to the network with adequate fees. When you are ready, you send it.
3. If you haven't broadcast it yet, only the copies you have made exist, and are not yet immutable. Once you have broadcast the transaction, it instantly exists on every node in the network, and once confirmed exists in every copy of the full blockchain. Your local copies also still exist and are what you should draw from in future. The copies in the ledger are there so that you can a) prove the data hasn't changed and b) get it back again if you ever lose your copy.