In version 7.5.0 WHMCS introduced default grace period and redemption grace period settings with the possibility to override these and set your own grace period(s) and fee(s).
The WHMCS documentation states "By default, we will automatically apply the default Grace Period for a TLD/extension when available. This allows customers to renew a domain past the expiry date for the given period of time. By default no additional fees are applied to the renewal of domains in the Grace Period, as is in keeping with the behaviour of most Registrar's and Registries, however you can set additional fees to be applied should you wish…"
Please read the WHMCS documentation for full details regarding how this operates.
In version 1.3.2 we added sections to the eNom TLDs tab giving you the possibility to have an overall view of the grace periods and redemption grace periods and any associated fees that have been set for the TLDs included in your pricing and to set these values directly from this page.
Once TLDs have been imported from eNom, the domain grace period and redemption grace period settings for the TLDs included in your pricing can be viewed in the table on the eNom TLDs tab.
These sections mirror the settings available in Setup->Products/Services->Domain Pricing and a change made in one will be mirrored in the other.
For details of the default grace or redemption grace periods, please consult the settings in Setup->Products/Services->Domain Pricing for the TLD in question.