Ask HN: Developer tests

Hello HN - I'm looking for Django / Frontend developers at the moment and devising a test for them to complete as part of the application process. What's a reasonable length of time to ask someone to give up to complete a test? Is 90 mins too much to ask?

The developer will be asked to complete this at home (it's a remote post)

Anyone got experience either being tested or testing potential hires?

It's a 16 week contract position we're talking about.

Cheers