Yes, first registration can be bit longer, dates back to when someone had to physically go and collect new tax discs and put them in the windscreen before you went to collect the car.
When it comes up for renewal, nowadays do it online, from about 14th of proceeding month, so should renew by 31 March, not wait until 1 April 2020 as DVLA computer will then flag as untaxed for a day. The DVLA will send you a renewal notice early March 2020 with renewal code to enter
Or you can still renew the hard way, and queue up in a bigger post office with a print out of your insurance document.
