If a placement is on or past it's start date, why would they not see the option to enter time when they log in to Back Office?
One reason an employee is not able to enter time is that they are set up with a VMS or Group time entry method, which doesn't allow for individuals to enter in time.
Also, if the employee has any onboarding documents that are required prior to time entry, they will not have access to the timesheets tab within their portal.