I have this meter as well, and our clock is about 15-20 minutes off what should be the the off-peak hours [in our case Economy 10] but just because the time is out, it doesn't actually affect the 'off peak' charges it's just that the loads on our off peak circuits [heating and hot water] come on 15-20 minutes later [but they also go off 15-20 minutes later] so there is still the same amount of 'off peak' time.
On our 5246C, it's very easy to know when the 'off-peak' clicks in [or out] as the meter under the stairs gives a loud audible click, which we can hear almost anywhere in the house!
The only problem, I'm currently having is that my electric company keeps wanting to change me to a smart meter [which I don't need or want] as I can see my electric usage through my solar+battery system which shows both real time generation/battery charging and load use in the house. The electric company has even sent me a message recently stating my 5246C will stop working when the BBC turns off the RTC signal but I'm pretty sure the 5246C doesn't rely on the RTC signal, it controls everything internally.
So, if you are concerned that your meter may be incorrect, you can always get your electric company to install a smart meter, as they are doing this for free as all the electric companies are well behind their UK Government set targets for smart meter installation.
Was quite a while ago though. What you see in the display cycle is set by the config file. To change that, you'll need an app called meter utility and a flag probe. Also the config file sets whether the meter clock adjusts to dst. Regarding the led, it will pulse while the meter is registering energy, but will come on solid after a while of non registration.
