After you make payment you'll get a webpage that says thank you for payment and you enjoy the benefits of the subscription from payment date.

As an aside, I have LM+ Lite from the AMEX Cardless Elite card. I paid on Nov 28 for LM+ Basic because I wanted to book a few flights with the ability to cancel for free (free cancellation of LifeMiles redemeptions is only possible with the Basic plan or higher). I got charged $30 on my AMEX Avianca card and got the website that I noted above - so I felt comfortable buying the ticket shortly after subscribing. I waited for many days but my LM+ plan page never changed to Basic, it stayed on "Lite" and I received 500 miles on Dec 4, which the day I receive my monthly LM+ miles benefit. I did not receive 2000 miles as is promised with the Basic plan. I called LifeMiles and they said to wait 30 days for it to be reflected on my account. I waited until Dec 28 - nothing changed. Suffice it to say I am still waiting to this day for resolution - they have a request in the system that they have not done anything with. At this point I don't care if it is a refund of my $30 or a retroactive application of the status. I just want resolution! I keep calling to get it bumped up in priority.