T4605 added backoff for repository polling. This is generally good but sometimes people really really like seeing updates right away. If there was an api to tell phabriactor that it's a good time to check on commits, it could be called when the repo was updated (ie in a hook). This would decrease update delay without extra polls. One part I am unsure of is how 'you should check now' polls should interact with the existing backoff polling.

(People could also probably control tradeoffs resource use vs time to update with a cap on max polling time, but this seemed like a more complete long term solution.)

FWIW This is the approach trac takes to know about git updates.