Hi Sid Mac,
Good to see you here. Hope you stick around.
Regarding the Tawny, the first couple of days will see it in pristine condition. Thats when the sudden burst of air can, and often does change the sublties of the taste. But with a good standard Tawny like you have, it should be a lovely drink for a few weeks in the conditions you have. I wouldn't be surprised if it was drinkable into the months.
There is a general concenous that the really old vintage ports, if they've survived for a 100 years plus, might give you a glorious hour or two, before fading fast. But thats not a concern here.
If you know for certain you are not going to drink it for say a couple of weeks, and you just want to preserve it, put a stopper in the bottle and put it in a very cool fridge. That will slow down any degredation to a minimum.
But now you know the generalities, and I'm sure others will chip in, I suspect that as you explore the site a bit more, you'll end up drinking this one a little bit quicker than you expected, causing this topic to be more theoretical, than practical.
Alan