Edit (Sept/3/19): I can't recommend this particular clock as mine broke in a few months. (yes I tried a new battery).

My bike computer doesn't have a time of day function so I made this to mount a cheap stick-on mini clock (https://www.ebay.com/itm/Mini-Luminous-Quartz-Analog-Watch-Stick-On-Clock-For-Car-Boat-Bike-Motorcycle/153417342367) to my handlebar. It's mounted via a zip tie that goes through an internal groove. Add a small piece of double sided tape and it's not going anywhere.

Should fit a variety of handlebars, from motorcycles to road bikes to MTBs.

Printed with PETG at .20mm with about 50% infill. Printed with the face side down with support touching the build plate. The internal grove for the ziptie printed fine without any support there.