You can allow students to submit hand-ins late by going to the assignment page and then select the Hand-ins tab. Scrolling down the page there is a list of students that have not handed in the assignment. To allow for late hand-in for all students click Allow all to hand in late or you can select which students hand in late by clicking Allow next to the student's name.
The same can be done to allow students to give feedback late by going to the Feedback tab on the assignment page.
Note: When you use "Allow all to hand in late" and set a deadline, you override any deadline you have set for students you have already allowed to hand-in late.
Similarly, if you choose "no deadline" when allowing all to hand in late, any deadlines you have set when allowing individual students to hand in late will be removed.
For example if you allow Lorelai to hand in late until Tuesday the 27th, but then later allow all to hand in late until Sunday the 25th, Lorelai will also have to hand in on Sunday the 25th at the latest. Similarly if you choose "no deadline" when allowing all to hand in late, Lorelai will also not have any deadline.