On time v. in time

On time means punctual, not late.
If something happens on time, it happens at the time which was planned.
• They’ll meet you at 9.30. -Okay, but tell them to be on time.
(= not to be late, to be there at 9.30)
• The 10.33 train left on time. (= it left at 10.33)
• The meetings were very well organised. They all began and finished on time.

The opposite of on time is late
• Be on time. Don’t be late.
• She is never on time. She’s always running late.

In time (for something / to do something) = soon enough

• Will she be home in time for lunch? (= soon enough for lunch)
• Hurry! I want to get home in time to watch my favourite soap opera.
(= soon enough to watch the soap opera)
• She’s sent him a birthday present. Let’s hope it arrives in time (for his birthday).
(= soon enough for his birthday)

The opposite of in time is too late
• I got home too late to watch my favourite soap opera.
• The present arrived too late, full three days after his birthday.

You can say just in time = almost too late
• We got to her house just in time to see her off.
• A car door swung open in front of me, but I swerved just in time to avoid it.