The last big animated movie Universal turned into a ride was Despicable Me. The Orlando ride opened two years after the first movie and one year before the second movie. It did have the advantage of being an overlay of an existing ride.
SLOP might take longer to build, but everything else looks similar to Despicable Me. Well, minus the minions. Having it ready in 2018 to make a lot of sense.
With Fast and Furious delayed one year Universal now has a major ride opening in 2018. Nintendo will open in 2020. This still leaves Universal Orlando without a major attraction opening in 2019 that we know of.
Secret life of pets might be held back to be the 2019 attraction. It could then be part of a modestly larger overlay of Toon Lagoon retail/food area, though the additional area might not be SLOP themed. There could still be a project that pops up, possibly going in to replace Shrek or T2 that would end up being the 2019 project and allowing SLOP to open in 2018 after all.