You must complete the interview before 23.59pm GMT on the day your interview is set to close. So if your closing date is 20 June, you have until 23.59 GMT on the evening of the 20th June to complete your interview by.
You can check timezones here https://www.timeanddate.com/worldclock/converter.html
If you fail to complete the interview before this time the interview will show as 'Expired'. You will no longer have access to the interview and you will have to contact the employer directly to ask about extending the deadline for you.
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