You can also do that too right now using text fields - in fact it’s even easier than times because Dataview automatically parses it into a duration for you:
Today I did stuff for `$=dv.current().read_for.plus(dv.current().exercised_for).as('hours')` hours.
Unless I’m not aware of some built-in SUM feature of Obsidian, you’re still going to need to use Dataview or some other Javascript to sum your fields, in which case you can already do that right now.