If you're keeping track at home, that's enough tokens to buy a single skin (around $5). So, you'll earn roughly 3 - 4 tokens per every hour you watch. If one team is getting its ass handed to it, the time investment will be much lower, of course. You'll have to link your Battle.net account with the Twitch, MLG or OverwatchLeague websites first, but regardless of where you play, console or PC, you'll be able to earn Tokens.
Naturally, Twitch has special for-pay emotes (Cheers and Bits) on tap that will unlock time-exclusive skins and team-branded items as well. In 2016, Bits generated some $6 million for Partnered streamers on the site. Additionally, Twitch is teasing a special VIP ticket of sorts that'll include more in-game rewards, behind-the-scenes video and more.
If you were wondering how long it'd take for Twitch to start cashing in on OWL's popularity, well, here you go. Maybe don't be too surprised when others follow suit.