Problem description: Two minor past date related issues exist in SLA configuration form:
1 - If a user creates an SLA with Excluded downtime older than 1970 (don't ask why) then no errors will appear, but when the user will attempt to edit this excluded downtime, then the following errors will be shown instead of the excluded downtime configuration form:

Incorrect value "-145677600" for "period_from" field.
Incorrect value "-145674000" for "period_to" field.

Example:

2 - Slightly different situation occurs if the Excluded downtime starts too far in the future - in this case the validation works only when he user attempts to save the created/updated SLA and not when adding the downtime to the SLA. Furthermore, when such future downtime is added to the SLA, the Start date is displayed incorrectly in "Excluded downtimes" table - it is displayed as the top limit of the allowed start time in the current moment.
Example:

The above two problems indicate that the Start date parameter is not validated when adding the Excluded downtime to SLA, but it should be, same as all other parameters in this dialog.

3 - In case if the user will attempt to use a date too far in the future in the SLA "Effective date" field, then there will be a normal error shown informing that the effective date is too large, but if the user enters a date prior to 01-01-1970, then a less user-friendly error message will be shown - see below. Suggestion is to use a similar error message as the one in case if the effective date is too large.

Invalid parameter "/1/effective_date": value must be one of 0-2147483647.

Example: