It can most certainly be used in the short term, but will in most cases only be giving short term signals.
While others may disagree, I think it can also be used in the longer term, but with one most important caveat. This is that the Advance-decline line seems to have a long term downward bias. many have observed this. I do not understand why it is so, but it does seem to be there.
What the bias means is that:
1. We can use it within a given bull market, but not between the tops of one bull market and the next.
2. If a given bull market is very protracted, we need to have a very clear divergence - a minor divergence that may be due to the downward bias should be treated with extreme caution.