In my study I have N animal subjects, and I want to examine if the latency to retrieve the treat has changed during the time of treatment. The latency to retrieve the treat was measured for each of animal subjects at four different time points (baseline, one month, two months and three months. Each animal was given 5 seconds to retrieve the treat, and the time (in seconds) was recorded. The subjects that did not retrieve the treat during the five seconds were marked as NA.
In my analysis I am using a repeated measures analysis were I am treating latency as continuous variable.
Is there a way I can Include NAs values in my analysis?
I thought of attributing NAs a value that is above the maximum time (above 5 seconds) is this correct?

Thank you and I would appreciate your help!