On our Phabricator installation we have different groups using Maniphest to schedule their work, with different expectations about the granularity of the "points" (time estimate) field of tasks. Even within one project the desired precision might vary between tasks: Sometimes a job roughly requires "N days", while other tasks can be estimated more precisely to a much shorter time, e.g. "M hours".
Maniphest currently allows to change the interpretation of the time estimate through the configuration value maniphest.points, which allows to change the field labels. On our instance we chose "days" as the granularity, but in more fine-granular tasks this results in estimates like "0.125 days" when we actually mean "1 hour" (8h per working day). Additionally, with people on the team, who work only a certain (small) number of hours per week, this results in meaningless estimates (they don't work 5 days per week, thus the term "day" is meaningless to them). On the other hand, an estimate of "32 hours" for a task would suggest a fine precision that is not actually intended, if we actually mean "roughly 4 days".
To accommodate this kind of variance within one installation and to add flexibility, I propose to allow non-numeric values for the Maniphest points field, to support values like 3d or 3d 5h or 5h. Counts of the same type (i.e. "d/days" or "h/hours") could be summed up on the Projects Workboard. The implementation would not even have to know about the concept of "days" and "hours" to carry out this aggregation.
Automatically aggregating "hours" into "days" could have undesired effects, as different installations (or groups on one installation) might have different assumptions how many hours make up one working day (e.g. one group/instance might have 8h working days, while all of the people in another group work only half-time and thus have 4h working days, etc.). Thus my proposal to only aggregate numbers of the same type (i.e. suffix), without applying a specific interpretation.