they had much longer to prepare

[GoodTaste]

[FONT=Source Sans Pro, sans-serif] [/FONT]“The speed of China's response was the crucial factor”, explains Gregory Poland, director of the Vaccine Research Group at the Mayo Clinic (Rochester, Minnesota, USA). “They moved very quickly to stop transmission. Other countries, even though they had much longer to prepare for the arrival of the virus, delayed their response and that meant they lost control”.
Source: The Lancet - China's successful control of COVID-19

Is the phrase "they had much longer to prepare" actually referring to "they had much longer time to prepare" - that is, "time" is omitted colloquically?

 

[5jj]

'Time' is not omitted. It would be incorrect.

We could say 'a much longer time' or 'much more time', with the same meaning as 'much longer'.

 

[GoodTaste]

Isn't the word "longer" an adjective? Why is "had + an adjective" grammatical? Is it simply idiomatic?