FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
With the firewall policy rule setting 'set schedule-timeout disabled', a FortiGate immediately forces the session to end when the 'Stop Time' of a recurring 'schedule' object is reached.

Additional configuration steps are required in order to keep the session active until is finished or expired.

Through the CLI, follow the steps given below:

1) Edit the firewall policy rule
# config firewall policy
# edit <ID of the policy>
# set schedule-timeout disabled
# set firewall-session-dirty check-new
# end

2) Edit system settings
# config system settings
# set firewall-session-dirty check-policy-option
# end

The status of the session will change to 'persistent' once the end time of the schedule is reached and the traffic continues flowing.