I think the 3 and 4 years you are talking about are probably the license terms of the licenses that were originally bought.
The 54 days is the most important because that's the time you have left before you have to renew your licenses.
You should know that Meraki automatically coterminates licenses (at the moment). Hence the single date, regardless of the 3 and 4 years.
Basically if at Jan 1st 2018 you bought 2 APs with 3 YR licenses, the expiry date would have been Jan 1st 2021.
If you buy 1 extra AP with a 3 YR license on Jan 1st 2019, the expiry date would not be Jan 1st 2021, it also wouldn't be Jan 1st 2022. But more something like Apr 1st 2021 because some of the value of the second license will be used to get the first license to co-terminate with the second one.
More info here:
https://documentation.meraki.com/zGeneral_Administration/Licensing/Cisco_Meraki_Licensing_Guidelines...
Edit: Wow, HodyCrouch has written about the exact same answer as me at about the same time. I'll leave it as having it twice can't hurt.