Welcome Marina. I've aways liked 'time span', tijdspanne(Du), because of all other definitions involved, such as duration of time, period, a while, an era, etc. it clearly expresses the stretchability time contains ( whatever time may be). In Dutch spannen means 'to stretch'.
On a clock five minutes is five minutes, but the sense of five minutes may vary from half a minute to half an hour. (roughly estimated)
A space of time I had not read or heard of before.
(thanks for the link tsuwm)