An easier method to the others posted above is to replay level 3.
to make things easier play on human difficulty and have at least Eryx. the reason for Eryx is that you can kill the shielded enemies far quicker than with arbiter. and the same goes for the chainsaw enemy too.
once all 5 enemies are dealt with go to were Kat has drawn the exit portal. normally you would have to go and get the angel jump ability. but you already have it (as this is a replay) so just angel jump across the gap and finish the level. time do vary from between 1:10 up to 1:45 was my slowest time.
Achievement hunters have done a video on this method so i have included it below ( strong language is used during this video)