"Vôo" doesn't have any circumflex...
It had, a few years ago, before the ortographic changes (2009)
How do you know when to use a before perder (like in não há tempo a perder)?
a perder, para perder, prepositions like to ( time to lose)
Would "eu não quero errar o voo" also be correct? Or does it have to be the verb "perder" when talking about missing a flight?
Yes, you have to use "Perder".
How do you pronounce "voo"
The first "o" is similar to the O in "goal", the second one sounds like "u" in Portuguese.
Ok now I'm confused with how to pronounce 'voo' 'vô' and 'vó'