Push the time back =時間を遅らせる
Push it back =遅らせる
どちらとも同じ意味です。時間の話をしてる事をお互い理解していればtimeと言わずにitでも伝わるはずです。
We're pushing back the meeting to 10 o'clock since everyone thought 9:30 was too earlier.
A: When's the meeting starting this week?
B: We pushed it back to 10 o'clock this time.
Start later =開始時間を延ばす
We're starting the meeting thirty minutes later than before because we got complaints that it was too early.