Yes, you setup office hrs within Settings -> Time, Office Hrs
Under the sip configuration within the 'Route Calls to', destination for calls outside of office hrs - forward to outside number.
On holidays - setup your holidays. Holidays use the Holiday digital receptionists to route calls.
Setup a dummy extension which will forward calls 'If I am busy or my phone is unregistered' forward calls to the mobile number
Under Hol IVR destination for invalid or no DTMF input call the dummy extension
On the outbound rules, the outbound call will be using a system account so create a rule with the prefix of the mobile number (no other entries) and place this near to top of the rules