Hello All!
      Is it possible to have gravity take effect at a certain time, as opposed to immediately?  That is, I want an object to fall to the ground at a specific time, as opposed to the moment the animation starts.

Object? What Object? That one? My jaw certainly dropped

On a serious note. Yes, you can do that to rigid physics objects. The Rigid Body type can be switched on a timeline (Rigid State).
You can have Static or Kinematic type at frame 1 and then switch to Dynamic at whatever frame you need the *object* to start falling.
After setting up, or changing Rigid State make sure to delete Animation clip for your object.

Thanks!  I had to substitute a rigid body for the soft cloth first, but it worked.  No way to do it with the latter?

No, I do not think you can do it with Soft Cloth Physics. It starts interaction the second you hit the Play.
I still do not understand what item you are referring to. What else is there left to fall: a bow, strings... ?

Well then my options are to switch out the thong for something rigid body, OR (just thought of this) to splice videos together!
MATURE WARNING  Video

Ahh, OK. Here is how:

Enable soft cloth and enable soft cloth baking in Project settings.
Place the scrabbler at the frame where thong has to go down.
Play in by Frame mode.
When done, disable soft cloth for the thong and play normally from the beginning in real time.

Just need to play with collision shapes and physics a bit for the *right* fall.
If you change girl animation, you'd have to bake soft cloth over again.

Here is a basic sample: