Lincoln picked the timing, and it appears he did so deliberately to avoid any issues with Congress telling him "no."
If you are going to deliberately start a war, best to do it when Congress cannot stop you.
Their actions were a rebellion in any sense of the word.
Not for a nation that was founded on the premises articulated in the Declaration of Independence. You may not have noticed, but Independence was listed as a right of man, therefore it was rebellion to oppose what they did.
Lincoln rebelled against the principles founded in that document "four score and seven years" earlier.
Also, "rebellion" is what servants do to masters. If England leaves the EU, it's not "rebellion", it's a peer state leaving a collection of other peer states.
Actually he did not. The House had recessed on March 3rd, the day before the inauguration. The Senate stayed in special session a few more days the confirm his cabinet appointments.
Not for a nation that was founded on the premises articulated in the Declaration of Independence.
In any definition of the word.