Dynamic Working patterns

I have a member of staff that wants to formalise a set pattern because of external commitments, is that possible?

It would be unwise to enter into an informal agreement with an individual that sets a formal pattern of working as the needs of the service/team are likely to vary over time. Staff and managers should create working arrangements that allow flexibility on both sides to achieve this. If staff request a pattern this should be handled through a flexible working request and managers should consult your HR partner for support. Dynamic Working arrangements are non-contractual and are subject to change.

Dynamic Working patterns may need to vary week-to-week for an individual so will a manager have to spend time each week confirming these decisions? 

This will depend on how the arrangements are implemented. Managers should be cautious about agreeing arrangements that create additional workload for either the manager or member of staff.