The Next Morning
Next Morning, The Following Morning
The next morning is the next morning.
The reading can be what you've learned with the kanji, よくあさ, or it can be the on'yomi reading across the board, よくちょう. Both are good to remember because よくちょう is more formal (you'll use that reading in writing more often) and よくあさ is more informal - you'll use that in speaking more often.
I’m afraid that your 9:00 p.m. foot-pressure massage has been pushed back to 9:30 tomorrow morning.