All direct objects that begin with cardinal numbers are non-specific. Cardinal numbers are 'one', 'two', 'three', etc. (not 'first', 'second', or 'third').
[FF](#/lesson/WordOrder.04) | [MANNER](#/lesson/WordOrder.14) | [DIROB](#/lesson/WordOrder.16) | [OV](#/lesson/WordOrder.24)
De leerlingen moesten | in korte tijd | drie opstellen | schrijven
The students had to write three essays within a short time.
Sometimes, it is not so obvious that the direct object is non-specific:
[FF](#/lesson/WordOrder.04) | [MANNER](#/lesson/WordOrder.14) | [DIROB](#/lesson/WordOrder.16) | [OV](#/lesson/WordOrder.24)
Mijn collega heeft | deze zomer | drie weken vakantie | opgenomen
This summer, my colleague took three weeks vacation.
We could argue that _drie weken vakantie_ is not specific as it does not specify _which_ three weeks of vacation. Just take it as a rule that all direct objects that begin with a cardinal number are non-specific. And so the direct object is placed at the end of the middle part.