In case this is useful to folks - in addition to geysertimes.org or Visitor Center at Old Faithful, NPS has an information line for latest geyser predictions: 307-344-2751 (Option 1: Old Faithful; Option 2: Other Geysers).
On the final day of my trip, I was looking for additional things to do and wanted to see if I was able to catch a less frequent eruption. Was able to make it to a Riverside eruption thanks to this info and waited 40min to see a 20-min eruption :).
Very useful when you don't have convenient Wi-Fi access but have some minimal-yet-enough-to-make-a-phone-call service. There are also little whiteboards in front of every eruptible geyser, but they are less frequently updated.
Another unrelated tip - there are area-specific day hike maps available upon request at each village's hotel front desk and visitor center. Some popular trailheads also have a brown metal box nearby with trail guides inside ($1 donation or return after use).
Have fun!!