It really depends on how fast those microbes you need grow. Under ideal circumstances, i believe they can double in number in 24 hours. So under those circumstances, yes you typically see a very rapid difference at the end of the process. For example
1 x 2 = 2
2 × 2 =4
4 × 2 = 8
8 × 2 = 16
16 x 2 =32
32 x 2 = 64
64 x 2 = 128
128 x 2 = 256
256 x 2 = 512
512 x 2 = 1024
1024 x 2 = 2048
2048 x 2 = 4096
Etc
So with this doubling of numbers, all the work is done at the end and you hardly notice the doubling at the beginning because the numbers are so small. But you need those initial small steps to accumulate over time so that you can get to the big numbers at the end.
But you arent at that ideal circumstances, you might only be getting a 50% improvement every day, 50% of those small numbers at the beginning is less noticable and it takes much longer for those small numbers to build up. Your tests are nowhere near accurate enough to differentiate one day to the next, you would probably need to compare one month to the next to see any appreciable difference.
Try and do the same exercise of increasing by 50% per day and see how much longer it takes to that 4000 number in my example.
You are seeing nitrite in your test, so your cycle has established to some degree, so you arent at the very beginning of those small numbers, but it takes time for those microbes to grow and establish in your filtration.
There are a few shortcuts you can take to get those small numbers up quicker, so you skip a lot of those early steps. For example the bacterial supplement you mention in one of your early post. Problem is, those products mostly dont work. The live bacteria are either already dead by the time you buy the product, or more likely they were never in the bottle to start with and you just bought a placebo. Some people report success, most people dont. If you want to spend money on these products then go for it, but you are probably wasting your money and could literally tip £100s in your tank to no effect. Another option is use some filter media from an already established aquarium filter if you know someone with an aquariun who would let you have a little. But these 2 options wont instantly cycle a tank, it just cuts down on some of those early steps as the microbes still need to grow and colonise throughout your filtration media.