Personally I think 1st 12-18 months are more about observing progress in implementation of tactical ideas. We need to see the vision of what the finished article might look like. We saw that with Klopp even if the results and league position weren’t always great in 1st 18 months. Starting point is better for Slot so I see alignment of a good league position and implementing tactical ideas as being inclusive.
We need to remember that even with Klopp it wasn't just constant progress - there were ups and downs.
In 15/16 we had lots of exciting matches and got to 2 finals, but our league form petered out and we finished outside the European places. In 16/17, after signing Mane, Wijnaldum and Matip, we started the season well, keeping pace with Chelsea until about November, but then we had a mid season wobble (especially in January). But we recovered well enough to grind out the results we needed to finish 4th. In 17/18, after buying Salah, Ox and Robertson, and promoting Trent to the first team, we had a string of poor results early on, and only got 13 points from our first 9 matches.
This coincided with Klopp's 2nd anniversary at the club and there were a number of articles comparing his record unfavourably with Rodgers' first 2 years. I never gave this any credence, as this included 2013/14, but I do remember thinking at the time 'If not even Jürgen Klopp can make us competitive in the league, then who can?' As it happened our form picked up, and especially after signing VVD in January and Fabinho and Alisson in the summer, we had 2 1/2 amazing seasons.
So we need to be ready to give Slot time, as long as we see a plan, and he shows that he learns from the inevitable mistakes.