No exact expiration date on colored contacts?

I ordered colored contacts from Hollywood Color Contacts and the pairs that I got last up to 90 days (3 months), but there's no exact date. It just says the number of months I can use them for. So when do I start counting down the days till its expiration date? When I first open it or when it gets delivered?
If my question isn't clear lets say I ordered 2 colored contacts each expiring after 3 months (with no specific date). Does that mean that they'll last me 6 months? Or 3 months? Is it ok if I opened one pair and used them for 3 months and open the other then use that for 3 months or will the second pair be considered expired?

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