Are there any time-sensitive events in Skyrim, whose occurrence is based on how many in-game days have passed? Or, to phrase it another way, are there any disadvantages to waiting out time indefinitely, as is often suggested for merchant restocking?
The only time-sensitive event is your marriage ceremony.
Once you've proposed to your Future Significant Other, you'll need to arrange the wedding.
After you've arrange the wedding, you have about 24 hours before the ceremony takes place (it always takes place between dawn and dusk, 6:00 AM - 6:00 PM).
However, if you do miss the ceremony, you can go to your Future Significant Other and ask for another chance.
The Blood on the Ice quest may fit some definition of time-based. I believe this happened very early in my game I believe the murder happened, but I basically ignored it because I was on other business.Everything I have read online, seems to indicate that I am screwed, and will never be able start/complete that or own property in Windhelm.
Yes, there are. For example, there is an Orc stronghold called Largashbur, where you start the Cursed Tribe quest. They are suffering from giant attacks and if you wait too long, later down the road their stronghold and tribe will be destroyed.
I suppose the dragons are a time sensitive event. They are not unique events, but they do spawn once a day or so if you progress on the main quest line.
Now whether waiting out affects the "dragon spawn interval" I can't say as I am myself not very far in the main quest.