Can I share the product different times during the same day?

No, you need at least 24 hours to share the same product

I have found issues related to the content sharing through Twitter.

Note: due to a change made by Twitter, you can not be sure that the tweets are published, so the coupons will be given even if the tweet is canceled. For more information about this change, please click here:https://twittercommunity.com/t/forthcoming-change-to-web-intent-events/54718

When the sharing is made through Google+, the coupons are not generated correctly.

the issue is known and it depends on a Google bug still not fixed.
For more information about the bug, please click here: https://code.google.com/p/google-plus-platform/issues/detail?id=232