If you don't mind pulling your phone out, IFTTT launched a new app called Do that just lets you push a button to "do" something on one of their channels. They have pre-made recipes for putting the current time into Google Spreadsheets etc. https://ifttt.com/recipes/227069-track-your-work-hours
I think IFTTT is working on a Pebble app as well, but it hasn't launched.