GIVE ANSWERS - English

In British English, neither would be correct. ”It’s high time” would not be typically used.

In American English, both are correct but convey different information.

”he was” is using the simple past form in this conditional statement. This is communicating the idea that ”him being more attentive = a good idea, especially for him”.

On the other hand, ”he were” is using the past subjunctive form. So, this is telling the wish/request of the speaker that ”he becomes more attentive”. It would more likely be used when the speaker is annoyed with him not being attentive.

I’ve heard many native speaker teachers of English claim that ’he was’ and ’he were’ mean the same thing”. Nonsense! They are clueless about the use of subjunctive in English and perhaps should not be teaching English to non-native speakers...