You can set the Timescales on a Task Usage by selecting the context sensitive menu Task Usage Settings > Timescale
This window controls the three header rows; Top tier, Middle tier and Bottom tier.
Each tier can be scaled to show dividers such as minutes, hours, days, weeks, thirds of months, months, quarters, half-years and years.
Note: You cannot set a tier to show a larger interval than a higher tier. If you do, a warning will be shown.
For each tier, you can select:
The unit used for a tier. You can select: minutes, hours, days, weeks, thirds of months, months, quarters, half-years and years.
Number of units per divider. For instance, selecting 7 days, could show:
The label determines how to format the dates for the project. Each unit has a unique set of possible labels (formats) to choose from. When switching units or when zooming, these may revert to their default values.
Align the label left, centered or right in the divider.