Grammar question: had vs. have had?

Question

in the sentence:

During my time there, I had an opportunity to swim and waterski many times.

or

During my time there, I have had an opportunity to swim and waterski many times.

Answer 1

During my time there, I had opportunities to swim and water ski many times.

During my time here, I have had opportunities to swim and water ski many times.

Both of yours are slightly incorrect.

Edit:

Both should use the plural "opportunities" to agree with "many times". In the second one, "here" should be used instead of "there" because "have had" implies that it's an ongoing circumstance and you could continue to have opportunities, but "there" indicates that you are no longer there.

Answer 2

You could really use both, but you need to change the 'an' to a 'the'

During my time there, I had THE opportunity to swim and waterski many times.  

Answer 3

The first sentence is correct, if you change "an opportunity" to "opportunities" or "the opportunity."

The second is incorrect.  Have had is present perfect, which means it can't be referenced to in the past.  Sentence two basically means that during your time there, you had the experience of having the opportunity to swim and waterski.  However, the experience is something you didn't have at the time--it's something you have now.  One solution, if you want to use present perfect, is to change it to: "Because of my time there, I have had..." etc.