Both of these sentences are correct. However, they have slightly different meanings (just a very small difference). The first sentence implies that sometimes you play too much on weekends and sometimes you don't. However, when you do play too much, then your father becomes "not happy". That is, your father becomes unhappy during the weekends when you play too much. This implies that his mood changes, but probably just for a short time. The second sentence implies that you usually or always play too much on weekends. Your father is usually or always not happy about this, even in the middle of the week, though he may be happy in general. That is, he disapproves, but it may not be enough to change his mood.

I don’t think it is incorrect, but the two sentences have slightly different meanings. The first sentence (with “when”) focuses on how your father feels (“unhappy”) at the specific time when you are playing too many online games. The second sentence suggests that your father is unhappy about the situation not just when you are playing to many games, but that it bothers him so much that he keeps thinking about it even at other times.

alancoots gave an excellent answer.

"when", as used in the first sentence, can also be more figuratively used for "under the circumstances" more than "at the same time". This means the actual meaning can be closer to the version with "that". Sentence like this come in at least two forms. When in the first form, we recognise that there may be an element of time involved, or not depending on context. Enjoy

england and france with relationship england with good bounders . what is the difference between two sentences ?