It seems like they collected 5 screen time data points[0] but only present analysis of the first, collected at 12 months of age.

Did I just miss the other analyses?

Assuming I didn't, is it too cynical of me to infer that they ran the numbers for the other data points but found no relationship? Suggesting that screen use after age 20 months or so is substanitially less harmful?

[0] Quoting from the paper: "When their child was aged 12 months, parents were asked to report the amount of time on average that the child spent on screens ... . Parents were asked the same question on their child’s screen time at 5 time points between ages 12 months and 54 months."