Depending on the project or client, there may be strict validation and timing values that have to be followed and can not be changed. As such these values will be pre-set, overriding any personal preferences you may have applied, and will be greyed out.
In these cases, you must ensure your subtitle translations are kept within these allowed values.
Further detail regarding these client specific guidelines should have been provided to you, but please contact [email protected] with any queries.