Can I take my time to do manoeuvres during driving test?

You can take as much time as you need as long as it doesn't become a serious inconvenience to other road users. If you're being excessively slow, it can cause frustration for other drivers and they may try to get pass you and thus create dangerous situations for everyone in the vicinity.

Just imagine you're trying to do a parallel park and you get stuck and there's someone behind you who's waiting and finally decides to overtake you in a rush and they didn't see the woman on the other side who was crossing the road and therefore they had to slam on their brakes hard and now your car and their car are completely blocking the road because another vehicle is in front...

You are not expected to complete a manoeuvre quick and you do NOT get scored higher for performing faster than others. However, observation is necessary when performing manoeuvres to make sure that it is safe at all times and getting the manoeuvre completed in the best way possible is the key to success.