Maybe, but I don't think TTL matters for speed of initial propagation. I do set it low when I first configure a website so I don't have to wait hours to correct a mistake I might not have noticed.
Yes. Statistically the most likely time to change a record is shortly after previously changing it. So it is a good idea to use a low TTL when you change it, then after a stability period raise the TTL as you are less likely to change it in the future.
