If I buy two codes and apply them at the same time will the counter of the days display 30 days left (and update when the time is up) or will it display the 60 (or more/less) days that I have added. Thanks in advance.
It will say the number of days you have paid for. In your case 60 days. Then the next day it will say 59 days etc.
It is impossible to apply two PBP or SMS PINs at the same time. You need to have less than 15 days of remaining membership to be able to apply another PIN. If you are not talking about PBP or SMS PINs then disregard the above paragraph and please say which payment method you are using.