Each subscription allows weekly or daily rank tracking. By default the accounts are set on weekly ranking. If you want to change this setting you can easily do it from the dashboard here:
The weekly rank tracking option allows you to track more keywords but at 7 days intervals.
The daily rank tracking option allows you to track less keywords but on a daily basis.
The number of keywords you can track are listed below, based on subscription.
If you need more than that you can always check a the custom subscription option.