[Homer_J_Simpson]

Probably last 6 weeks, 90 days tops.

[BroJoeK]

"Probably last 6 weeks, 90 days tops."

For the first time here I've seen an explanation of why Lincoln chose July 4 to call back Congress.

"Lincoln called for troops to serve only ninety days not because he believed that the war would be over quickly but because a 1795 law limited a call-up of militia to not more than thirty days after the assembling of Congress.
With Congress called into session on July 4, the volunteer force would have to be disbanded by August 4.
He could have convened Congress earlier, but that would have meant an even shorter term of service for the volunteers."
David Herbert Donald, Lincoln