What is your 100/200m times as that will be a good predictor of what times you will be able to achieve with your program. Without wanting to put a downer on it but don’t necessarily expect to be able to automatically jump to a 50/51 time as it is a lot harder than it sounds.
I started doing 400’s last season and have only really started training properly for it this season and it is very hard going. I came from more of a speed background rather than endurance, I ran 11.0 for my pb for 100 (though realistically more like 11.2/3 as it was windy) and 22.8s for 200m so I assumed naturally I would be able to do sub 50 relatively easily! No chance ha!
I ran 51.4 once last year and a couple of 51.9s and they felt bloody hard! Its only now when I train with a 400m group that I realise how much strength you actually need to run a good 4 and how much fitness I lack…
I think personally it takes at least a year of specific training to get yourself up to a decent fitness level where you can run to the potential of your 100/200 times.
What I am trying to say (in a long winded way!) is that if you are basing the success of your program on say running 51s or on a specific time, don’t expect too much too soon and don’t write off your program just becasuse you aren’t getting the results you expected i.e 51s or whatever.