Where are settings for drag-and-drop touchpad behavior?

Check the output of synclient -l | grep -i drag. You'll see something like this:

LockedDrags             = 0
LockedDragTimeout       = 5000
TapAndDragGesture       = 1

I think LockedDragTimeout is the setting you want. To change it temporarily, run synclient LockedDragTimeout=value. Once you are happy with the value, add the command to startup applications.

To expand on mikewhatever's answer:

synclient TapAndDragGesture=1 LockedDrags=1 LockedDragTimeout=200

should do the trick temporarily. Specifically, you need the LockedDrags=1 option to enable them.

• TapAndDragGesture=1 ensures that tap-and-drag gestures are enabled (just in case).
• LockedDrags=1 enables locked drags (locks drag-and-drop until you tap again or a timeout happens).
• LockedDragTimeout=200 lowers the locked drag timeout from 5000 ms (default) to 200. If left at 5000, drag-and-drop will be locked until you tap on the touchpad (or wait 5 seconds).

For more info, run man synaptics. For a list of available options and their current values, run synclient -l. Once you have figured out your favorite settings, add them to a startup script as mikewhatever suggests.