I've noticed this with the default install-plans of GHC 7.4/7.6 (but not with GHC < 7.4 or GHC >= 7.8) and it looks like:
Preprocessing library rss-3000.2.0.6...
[1 of 1] Compiling Text.RSS ( Text/RSS.hs, /tmp/rss-3000.2.0.6/dist-newstyle/build/x86_64-linux/ghc-7.4.2/rss-3000.2.0.6/build/Text/RSS.o )
Text/RSS.hs:67:1:
Data.Time.Clock: Can't be safely imported!
The module itself isn't safe.
Text/RSS.hs:68:1:
Data.Time.Format: Can't be safely imported!
The module itself isn't safe.
After a bit more investigation, this appears to be a problem with the time < 1.4.2 range (and only for GHC >= 7.4); but I'm still investigating (this commit here for which time-1.4.2 was the first release to contain it seems relevant: haskell/time@7cc0d01)