Sometimes- happen often/frequently (eg: i visit my Grandma sometimes.) Someday- will happen in the future, (eg: I will go to Paris someday.)

They are actually not the same. For example, one chould say there are times when I feel like crying. Not quite the same as sometimes. Or there comes a day when I'll win, not quite the same as someday.

There are times when- says, "this happens sometimes, and it will happen in the future at times. There comes a day when- says, "this will likely happen to each person sometime, once- and imagines this activity in the future." This activity is imagined as an important point in the life of the person. Someday= over a long period. Likely years. Sometime= minutes up to years. Not likely years.

Yes they are the same thing but, it depends on how you use them because when you want to use it singularly you have to change the verb. For example1: There are times when I feel really sleepy = Sometimes I feel really sleepy.