3 days a week.

My advice?

Go to Jerez, Cadiz or Ronda instead.

If you insist on going to Gib, as someone else mentioned, go for a day.

Edit: just be careful with the weather if you're going the top of the rock. My app says cloudy Saturday and Sunday, which can often mean the top is enveloped. You also occasionally get the levante in this time of year which will involve low lying cloud early morning until the sun burns it away.