Fix input validation in Timer

[cydanil]

Description

closes #285, where the timer was reported to add zeroes and not validating the input correctly.

Values can now be at most 59 (hours, minutes, seconds).

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.