IIRC there are two types of OSU processes, depending on what your bank has agreed to pay Intuit. One is slower than the other. That may have something to do with it.
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The two connection methods are: Direct Connect and Express Web Connect.
I've never tried to time either one (I don't use Express Web Connect), but just knowing what Express Web Connect "may" have to do (screen scrape from your financial institution's web site), I'd say EWC could easily be slower than Direct Connect.
If the problem lies with one financial institution, you'd have to determine that by process of elimination. Use "Update Now" for each financial institution and time the results. Or, as suggested, you could probably get the timings from the Quicken CONNLOG (Help > Log Files).
If no financial institution seems to be the culprit; try eliminating the download of quotes from OSU. Also eliminate updating of Quicken.com, and the downloading of currency exchange rates.
[My Q2013 download times are no slower than my Q2010 download times.]