You can only take a second offer if you're in the last 30 days of your existing offer. (This applies even if you've cancelled your Pass.) So if your current offer has more than 30 days left to run, you won't be eligible for this deal."
This is the situation I am in - my current offer expires on 24 August, so I'm able to take up this offer, which then kicks in from 24 August through to 24 June 2019.