guys i did a minor fuck up..... delayed the timeline of the project..... client will call in 6 hours .... i'm covering the damage ...but in meantime ..... what should i say to him when he calls ..?
"Sorry for the confusion" ?
"Thanks for understanding" ?

Don't answer. Just disappear. Works best in my experience. You get to crack a cold one while leaving the worrying to the client. Afterwards he will be so pleased when you finally contact him that he'll be willing to forgive anything and worship you as a god.

...

But seriously, ask for an extension. Projects always take longer than planned. That means working overtime though.

Apologise and explain why its delayed. Best to be honest. Give them realistic new timescales. They might complain now but will probably come round. Been in a similar situation a few times and its amazing how well some clients take it. As long as the end product more than meets their expectations you should be ok in the end

I had no clear Unix timestamp for the delivery date.

Exaggerate then compensate. Exaggerate why the deadline was not achieved, compensate to:
1. Make your exaggeration believable (people tend to give up on things more easily when another "big" problem is passing by)
2. Not actually loose the client

But if you think the client is good enough just say the truth. Ask for an extension and say thank you.