The 22 minute wait at Guildford in the evening is because there isn't a clear path before then without impeading other passenger services. The 16 minutes of pathing allowances is to make sure it doesn't run into the back of other passenger services, not slack to help it make up time.
If you start earlier, you run into the back of 2P91 pretty quickly. That means you effectively take up 1P59's slot at Haslemere. Once at Havant, you impead on 1C95, which in turn shunts 1P59 back (again). You then end up in a situation where 4 trains (1T57 at Portcreek Junction) have to be shunted back to include this once-per-day additional train. You'd have no platforms at Portsmouth Harbour, a 15 minute turnaround at Southsea (that's going to be reliable(!)).
It's 7pm, and peak time services from London are rammed, and yet you want to mess a load of them up to include this far less busy service.