You can purchase one anytime, but depending on when it expires is what you have to look at, sometimes you will purchase it with a month left to use it and have to renew it, if your question was what time during the day, if there is a specific time, it does not matter they are open 24/7
The same as Walmart's regular opening hours.
This Wal-Mart is open 24 hours 7 days a week.
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