Hi Trevor,
There are multiple formulas you can write to accomplish this, but it will depend on the time duration you would like to find the maximum for. In the photo, I have found the maximum of my signal Temperature over 2 different time ranges. In this case, the dashed line is due to uncertainty in the calculation, but both formulas result in Signals.
1. max of 6 hour periods: This formula will find the maximum point in every 6 hour window: $t.aggregate(maxValue(), periods(6hours), durationkey())
2. max of the last 6 hours: This will use now() so that the maximum is calculated for the past 6 hours relative to current time: $t.aggregate(maxValue(), condition(6h, capsule(now()-6h, now())), durationkey())