The values you enter in the Budgeted or Planned Units and Remaining (Early) Units fields are converted to the Unit/Time specified in the User Preferences, Time Units tab. For example, if the Unit/Time user preference is set to Hour and you enter 1d, the value is converted to 8h. To avoid planning mistakes, you should set the Unit/Time user preference to the same time unit you use to plan your work. For example, if you plan your work in hours, set the Unit/Time to Hours.
Additionally, your user preference setting for 'Interval for time-distributed resource calculations' (User Preferences, Resource Analysis tab) determines the minimum timescale interval in which you can enter or edit data. For example, if this option is set to Week, you can only enter or edit data in weekly, monthly, quarterly, or financial period timescale buckets. When you display timescale intervals smaller than the interval specified as your user preference, the buckets are not editable. Using this case as an example, if you display daily timescale intervals, the buckets are not editable.