Sometime vs. Sometimes vs. Some time vs. Some times

Sometime is an adverb that means 'at an unspecified time in the future'. We use it to mean that something happens only once in a random manner. Sometime is almost the same as 'Someday'. 

I want to go shopping with you sometime.

My brother's flight arrives sometime next week.

Sometimes is an adverb that means often, now and then, frequently, or occasionally. So we use it when something happens more than once repeatedly. 

I forget to take my medicine sometimes.

Sometimes I take a nap after launch.

Some time is a noun phrase where time is an uncountable noun. Therefore, Some time means a period of time or a time span (usually long). 

Please stay with me for some time.

This large file will take some time to download.

Some times is a noun phrase where the time is a countable plural noun. So Some times means an unspecified number of instances or occurrences. 

There will be some times when your life will turn upside down. 

Some times in my time was very stressful.