online ticket seller’s late delivery notice

I recently purchased concert tickets for the 1st time from ticket.co.jp, for a show happening in a week's time on 16 june. Seller was suppose to mail the tickets tomorrow 9 june (one week from show date)

I just received notice that seller will be mailing the tickets late, on 12 june, 4 days before the show.
This is making me nervous.

Will the tickets arrive in time?
How much time leeway should i give seller before i contact ticket.co.jp if delivery notice not received?
What should i take note of, steps i need to do to ensure i get a refund back if seller screws up?

How long it would take really depends on where you and the ticket seller are and what method the seller is to send the ticket.
If both of you are in Japan and the seller will send the ticket by Japan post, it should take only 1-2 days, so you would be able to receive it on 13th or 14th June.
If the seller use kakitome (registered mail), you can trace it, otherwise there's nothing you can do to check the delivery situation.

thanks for the reply. it's my first time using the website so any help is appreciated for me to understand the process better.

we are both in Japan, seller is suppose to mail to my hotel.

if delivery takes 1-2 days, is that a good time leeway where if I don't receive or hear from seller after that time, I should be able to cancel the transaction through ticket.co.jp, receive a refund and/or complain about the seller?

I have no experience with ticket.co.jp but checked it up and found some guide lines.
It is not allowed for seller to use ordinary post service, they 'must' use registered mail or domestic courier service, that means you can get the tracking number.

Also it stipulates that you can cancel it if you do not receive the ticket within 4 days prior to the date of the concert (in special case 2 days.)

You should ask the seller what service he/she uses, and its tracking number so you can check from your side, and if you do not get the ticket in time, you can claim cancellation/refund.