It’ll be all right on the night
Definition 1 of 1
Pro Tip 1/3Positive Reassurance
Used to encourage someone by suggesting that any current issues will not affect the final outcome. 
The stage lights malfunctioned, but the manager assured us 'it’ll be all right on the night'.
Pro Tip 2/3Performance Focus
The phrase emphasizes that the actual event is what really matters, not the lead-up to it. 
Our costumes aren't ready yet, but the designer said 'it’ll be all right on the night'.
Pro Tip 3/3British Origin
Understand it's a British English phrase, so it might not be well-known in other English-speaking regions. 
When I studied in the UK, my classmates often said 'it’ll be all right on the night' before exams.