The Coppock is used on a monthly chart. That was the way it was designed and the way it seems to work best. I do see people using it on weekly and daily charts, but I am not convinced that it has much merit compared to other more mainstream momentum oscillators. This is especially so on individual stocks. The Coppock was designed for mass-market indexes and seems to work best that way.
The signal for the long term investor to get back into the market is when the Coppock turns up from below the zero line (i.e. is negative and becomes less negative).
You will notice that the Coppock has occasionally given a misleading signal, one of which was earlier this year on the Dow (but not the S&P or Nasdaq). However, its record is very good, testing it back 100 years.