With a time expression, we use later to mean after that time, and in to mean after now. But without a time expression, we can use later to mean after now.
She was taken to the emergency room in the morning and given some basic treatment. She was released a few hours later. [time expression + after that time = later]
Mr Gui is not back from his vacation yet. Can you call back in a few days? [time expression + after now = in]
Could we talk later? [no time expression = later to mean after now]