You can "split" a multi-day booking in two or more bookings by highlighting the day or days (in Hourline click at date on top, or in Long Form select the days) you want the booking to be split on > click on booking menu > split > confirm.
IMPORTANT! Do not to select the first day of the booking!
Result is two or more bookings - one from the start of the original booking to the day before the highlighted day, the other from the highlighted day to the end of the booking (booking name, status, custom fields, involved objects, etc - all remain identical for both bookings).
Time Reports and Extras in Time Report
If some days of the multi-day booking have been time reported, they remain time reported.
If Extras have been added to specific days of the Time Report the Extras will "stick" to that day.
If using predefined Services or ad-hoc Extras, when splitting the extra will remain on the day it was added. You might have to add to the split bookings again if you need it.