Any individual Spot (job/item/shift) can span overnight. For example, if you have a shift that starts at 9pm on Saturday and ends at 1:30am on Sunday, you will set the Start time for the Spot at 9pm then the end time at 1:30am. The system will pop-up a warning that that the start time appears to be earlier than the end time - just proceed to choosing your date (Saturday).
In the Spot's extra details, write a note that says "OVERNIGHT SHIFT" to make it extra clear to the person signing up that this shift spans midnight.
If you are Adding Shifts in a series and one Shift spans past midnight, just end your series of shifts one shift short of the midnight shift and add your last overnight shift separately after saving the series.