Client Side Validation gem - adding custom validator for select

Dear All,

I have two select tags.
Start time and end time select tag.
I am using client side validation gem in the form.
I need to check if the start time select tag has value less than the end time select tag, using a custom validator.

Is there a way to achieve this in the client_side_validation gem.
Or is there any other better way to do it.
I need error message just like the client side validation gem.