I have seen requests for a faster refresh time, but changing the refresh time for everyone would have a huge impact on traffic and could lead to everyone being slowed down. Going through all of your calendar feeds one by one can be tedious since it is a matter of hitting the button, waiting 30 seconds or so, and then hitting the next one. With 20 or 30 feeds this becomes a good amount of time spent just waiting for the refresh to complete.
Being able to either:
A - Just click a single refresh all button
B - Select check boxes and then hit the refresh button to refresh selected feeds
And then let them go through one by one on their own would be a huge time saver for anyone who needs on demand updating but doesn't have time to sit and watch the refresh take place.
Doing something else and coming back doesn't really work since you will inevitably come back too early or long after it is finished and this again stands in the way of this updating being "on demand".