Use date fields for from/to filter

sklement , Try a measure like

calculate(countx(filter(worklogs, worklogs[SprintName] = max(Sprints[SprintName]) && worklogs[Timestamp] >= Min(Sprints[SprintStartDate]) && worklogs[Timestamp] <= max(Sprints[SprintEndDate])),worklogs[SprintName]), values(worklogs[SprintName]))

Hi sklement,

I'd like to suggest you take a look at the following link about use 'crossjoin' function to expand the date fields, then you can simply mapping records with detailed date records for analysis.

Solved: Spread revenue across period based on start and en... - Microsoft Power BI Community

Regards,
Xiaoxin Sheng