Hi Jenni thanks for posting in the community.

You can change the font size and appearance in an interval by selecting the text and using the font action menu at the top of your document.

I hope this helps! Please let me know if you have anymore questions.

Thank you Ashely however this appears to only change the text in the interval and not the date of the the interval. I see how to change the format of the date i.e. 1/31 or Jan-31 but not the formatting of the date such as the size font or color. It doesn't change with the task name - is it even possible?. 

Thank you for the clarification! You're right it's not possible to change the date in the timeline interval. Would you mind adding your idea to our Product Feedback section? Ideas submitted are passed on to the product development team for their consideration.

The workaround of layering text blocks is one option that could work. Another option I'd like to suggest is to use a shape from the standard shape library and add your text to that (a text box may also work). Once you adjust the size of the shape you can move it to the timeline and the date won't be automatically added in.

I hope this helps! Please let me know if you have anymore questions.