Another multiple system question

Hi everyone, wasn't quite sure where to put this but since it seems more of a technicality with mogstation possibly that I'd put it here.

I currently play on PS3 (will be switching to PS4 when available), but my brother is an avid gamer like myself so we both battle for time with the TV. I thought rather than battle this out I could get a second license for my mac (bootcamp to windows) and play on there while he plays whatever on xbox/ps3 etc.
Let me clarify he doesn't play ffxiv so I'm not trying to get multiple people playing simultaneously.

However I'm a little hazy on the details behind the process and what I'm paying for with the second license. I understand that I need a windows license as it's a different client, which is fair enough, but I'm wondering if there is an option to just buy the license. I bought the PS3 version for £9. Now I'm looking at PC and it's £20, so I imagine £9 of that is really the subscription cost for the free 30 day trial while the rest is the license for the client.

tl,dr: If I get the £20 pc download, will I get an extra 30 days subscription applied to my service account? If not, is there anyway I can just purchase a windows license, free from the trial? It just seems a waste of £20 if nearly half is a free trial I won't get.

Thanks for looking, hope it's easy to understand what I'm asking and if it's in the wrong place I apologise, mods feel free to move it.

All new license, comes with 30 days game time.

Ah so it's not just a trial period, it's actual game time just as a normal subscription would be? So for example if I had 90 days then I'd have 120 days with the new license added?

If you already have an active account, the time included will be added to your existing game time. If you are new to the game, or setting up new SE account or Service Account, then that game time will be applied to them (new).

I won't call it trial period, it's game time.

Ah that makes sense, I've got a service account with my ps3 version with 90 days on it. Thank you so much, couldn't find any specifics when I searched for it.

For more clarification:

I owned Final Fantasy XIV on PC. I bought a PS3 copy and applied the key to my PC account which lets me play the same account on both platforms. I got 30 days added to existing game time.