Aggregating timer metrics to get max value

Hello all,

I am trying to execute query where i get the max value of timer’s max over a certain period of time. I was initially using the max(increase(max_metric{}[$__range])) by (clientName), but have gotten incorrect data because increase can only be used for counter functions. I have tried using max_over_time but need to be able to group by the clientName which seems unallowed for this query. What is the potential solution to getting a max and grouping timer data over a period of time?