I've seen the complete schedule - naturally one can't know if they will be on time. Just before 10 Katy Perry is to perform, followed by 10 Chelsea introducing Hillary. Chloe is 3 speakers before that, so you can sort of guess at the approximate time.
There's a whole lineup of speakers, many governors, mayors, senators etc. from around 4:30 throughout out the night - so it's amazing that she is not only speaking, but has such a late and prominent time.