In short, it went a lot better than last year.
The biggest mistake I made all day was first thing, when I left my flat without my newly updated door position sheet. That was going to make things interesting! Fortunately I've done enough chanlenging already to know some of the door positions by heart, plus I had a not-very-good app on my phone, but this would still put me at a disadvantage.
My initial plan from Borough was to hear north to London Bridge and then knock out all of the stations south of the river first then head north from Vauxhall, but I didn't like the idea of having so many changes early on. Eventually I found a route I liked with started with me heading south instead, as follows:
Borough

Kennington

BPS

(run) Vauxhall

Victoria

Sloane Square

Aldgates

Paddington

Lambeth North

Waterloo

London Bridge

Euston

TCR

Queensway

(run) Bayswater

Earl's Court

Russell Square

Holborn

St. Paul's
Starting on the first train after 1pm was an interesting one. A southbound train came in at 1 minute to, and all the challengers on this platform wondered if it would leave after 13:00:00. As it happened, the doors locked locked at about 12:59:57, with none of us on it, and a 6 minute wait until the next train.
Finally getting started, it was myself, Team Ian and Muadh heading south. Team Ian left us at E&C, and Muadh and myself changed for a Battersea train at Kennington, which came along after about 4 minutes. Down to BPS and he ran for the train back in the adjacent platform, along with a load of challengers in the next carriage along. I have no idea where they came from! I myself exited for the usual run to Vauxhall. I saw Milo and Yifan on the approach to Vauxhall, having clearly just run there from Nine Elms. In fact, there were a lot of challengers waiting on the nouthbound Vauxhall platform who had got there one way of the other. We all headed to Victoria together and had a proper race up the escalators to the westbound sub-surface platforms. Most of us made the tight connection, but only two - Milo and myself - walked down the train to make the second tight connection at Sloane Square.
The pair of us were on a circle line train heading east. I contemplated dropping back a train for a better chance of getting north of the Aldgates quickly, like I did 2 years ago. The difference was that I then wanted to head to Paddington, so ending up on a Met wouldn't be good, and the next circle was most likely some way behind (although I didn't check). I decided to gamble on a H&C from Aldgate East, as did Milo. He took off like a rocket at Aldgate, with me trailing behind. I made it to Aldgate East to see a H&C in the westbound platform.
We left straightaway but the got delayed going back past Aldgate as they regulated the service. Milo and I were in different carriages so I don't know when he got off the train. I went on to Paddington Bishops Road without incident then ran to Praed Street and took the Bakerloo south. Fairly swift double back at Lambeth North and (I think) decent connections at Waterloo and London Bridge.
My door position app only gave positions for the Charing Cross branch on the Northern line at Euston so I had to guess door positions, at which I got lucky. I knew it wouldn't tell me about the secret cut throughs at TCR and I was sure that I needed to be at one end of the train. I was then rather surprised when I ran up the stairs and found myself at the bottom of the main escalators. In a state of panic I followed the only Central Line sign I could see... and found myself back on the Northern line platforms. Thinking that it must be the other end of the platform I needed, I headed that way and things started to look familiar. Made it to the Central line just as a train was pulling in, which would mean - remarkably - that I didn't go down a train here.
Headed west and got out at Queensway for the usual run. A 3 minute wait at Bayswater, which was the longest wait I'd had so far, but a marked improvement on last year, and it was a Wimbleware, which was what I wanted. On the train Andi came down and found me. He must have been on the Central line train behind me and had just made this train. We both went down to Earl's Court and then up to Russell Square, with Andi telling anyone who'd listen about what we were doing.
Andi finished at Russell Square, and he very kindly agreed to buy me a pint so I had one waiting when I got to the pub. I finally made a good Russell Square connection on a Z1 challenge but then had another 3 minute wait for my final train. The doors were held shut for an agonising few seconds before I could finally stop my clock for a new Z1 PB.