Steps to reproduce:

1. Navigate to Monitoring -> Problems -> Create custom filter
2. Click on the cogwheel button in the filter tab -> In the modal, select Override time period selector
3. Add random values or remove all values in From/To inputs, click Save

Result:
See screenshots

Expected:

1. Consistent labels:

• Ensure that the error message texts match the field names in the form.

2. Offer assistance directly in the form:

• Provide hints for inputs requiring specific values, such as 'now/M-3d+1M/M' directly next to the corresponding fields or in an accessible tooltip.
• Provide examples of correct input values nad format.

3. Highlight affected fields:

• Describe errors in text form and identify the affected field. The cursor must
  be placed in the incorrect input field.
• Error messages should be descriptive and help users recover from errors.

4. Screen reader output:

• Ensure that all error messages are descriptive and accessible by screen readers.

5. Use of color coding

• Use color highlights only in addition to textual information.

6. If possible, implement client-side validation

• Verify the field values in real time and across all fields before
  the form is submitted.
• Immediately display and describe errors.