When you are granted an O Licence, or renew it, it is valid for 5 years.
There are two sets of fees to consider with regard to the O Licence. The cost for the licence, which is currently £336 for five years, and you pay for the full five years in one go. Then there is the cost for each vehicle which you can either pay for the full five years, £180, or pay for a year at a time, £44. Yearly payments are paid on the anniversary of the end of the month preceding the month in which the licence was issued. The payment is for the coming year. There is also a fee per quarter if you add a vehicle partway into the full year, £9 a quarter if you are adding it for the remainder of the licence duration or £11 per quarter if adding for the remainder of a year.
I’ve only ever paid for the full five years of the vehicle in one go, but thinking about it now I guess if some of the fleet was paid for 5 years and some yearly then trucks on the same O Licence could have a different expiry date on their licence discs. It would however be the same month end on each disc, just there could be a difference of up to 4 full years.