長くしました: Make long or make longer?

Question

Regarding panda viewing times at Ueno zoo:

動物園はたくさんの人に見てもらうために、シャンシャンを見ることができる時間を２時間半長くしました。
The zoo has made the time when you can see the panda two and a half hours long(er) so that lots of people can see it.

From the context it's clear to me that this is supposed to be 2.5 hours longer rather than 2.5 hours long, but how would the grammar change to express a fixed period of 2 hours rather than an extension of two hours?

I guess I would have expected the current sentence to mean long and would have expected something like 前のより長くしました for longer.

Answer 1

As 長くする means 'to lengthen', I do not see any ambiguity in this phrasing.

長くなる would be used to say 'become lengthened'. By comparison to 長くする the only real difference is between direct and indirect (transitive/intransitive) usage.

前より could be used, but would be unnecessary, as we can already glean that inference from the context.

If, on the other hand, you wanted to say that they 'changed it to' a viewing period of (only) 2.5 hours, you would say 「見ることができる時間を2.5時間にしました。」.

To say that they 'shortened the time' by 2.5 hours: 「見ることができる時間を2.5時間短くしました。」or 「～時間を2.5時間短縮しました」 or 「～時間が2.5時間短縮されました。」.

So, ultimately, the translation should read more directly as:

動物園はたくさんの人に見てもらうために、シャンシャンを見ることができる時間を２時間半長くしました。

So as to increase attendance (viewership), the zoo has lengthened the hours when 'Shan-Shan' can be viewed by 2.5 hours.