"She ran the marathon in less than five hours."
Translation:Zij liep de marathon in minder dan vijf uur.
'ze heeft de marathon in minder dan vijf uren gelopen' is that incorrect?
If you replace uren by uur it's correct. We don't use the plural of uur to indicate a time length, only when separate instances of an hour are meant and for quantifiers (when the exact amount is not known), e.g.
- de eerste twee uren gingen goed = the first two hours went well (two instances of an hour are meant)
- de eerste twee uur ging goed = the first two hours went well (a time length of two hours is meant)
- het ging twee uur goed = it went well for two hours (time length)
- honderden uren = hundreds of hours (quantifier)
- enkele uren = some hours (quantifier)
Kwartier (quarter/15 minutes) and jaar (year) are handled in the same way as uur, these 3 are the exceptions. All the other time units (second, minute, day, century, millennium, etc.) use the plural form whenever there is more than one.