Interesting idea, but I see a "time bar" as a sort of "best guess." Like you get from any MS install. Those numbers are never right. I'm promoting this, but I don't think that you will get a good number from the time bar.

Gregg, I understand that and it truly does take seconds sometimes, but when it doesn't, man that sucks.

Or maybe there could just be an initial guess as to how long it should take and if it's going to be over some time (like 5 minutes), pop up a warning box with the estimate and ask if you want to continue.

Bandwidth is the true issue here and as Gregg mentioned a wildcard, making an attempt at estimating duration almost futile.

Perhaps a histogram showcasing percentage completed of bandwidth for the task with a running stopwatch--different than guesstimating how much till finished. (Perhaps a semantic but speaks to what happened versus what might happen.)

Example, based upon your operations, you have 200MB needing creation. At point <x>, I have completed 75% of that 200MB and to this point, it took 00:15:23.35 to complete. This might be useful, and be plausible. Similar to a web file download scale--which are more accurate than the MS Installer bar graphs.