Reports are saying that the demand is lower than something like Mine Train or Flight of Passage, but the in-park rope drop execution is less well-organized. So yes, to avoid waiting 60+ minutes in the queue line for Slinky Dog Dash, the recommendation is to arrive at the tapstyles 45-60 minutes before the park opens to be ahead of the pack. You are basically going to wait 60+ minutes either way, though, so its your call.
Another popular suggestion is to ride last thing at the end of the night, and you might find a shorter wait, closer to 30-45 minutes. But I wouldn't want to miss Fantasmic or the Star Wars Fireworks to ride Slinky Dog Dash - so that option doesn't really work for us.