Is there a way to remove numbers in the time dropdown?

Unfortunately, there's no option in the form builder that will let you remove the numbers. A workaround would be to get your form source codes (http://www.jotform.com/help/104-How-to-get-the-Full-Source-Code-of-your-Form) and manually remove the numbers. Note that you have to embed the form using the modified source codes because there's no way you can import back the codes in the form builder. You also need to do the same steps every time you'll make some changes in the form.

Or, you can use a Dropdown field as your Time Selector.

Thanks