There should be no ‘hopefully’ get through the first 10 minutes. It should be something you’ve done in one of the higher % sweet spot workouts and know (as much as you ever can) is doable - from there you kick up to hopefully a real threshold (as mentioned, you’ll know if it isn’t as you won’t last 30 minutes) and then either ride out the time for a long TTE, or - if you feel you could go slightly harder - ramp slowly until you feel ‘over threshold’ …failure won’t be far away at that stage 