In British television the phrase "teatime slot" refers to the hours between 5 pm and 7pm. Initially, this was a period each evening during which the BBC showed no television at all – the so-called 'toddler's truce'.
In time, the BBC began to show television shows in this time slot, but with an emphasis on family entertainment.
The phrase is a reference to tea as the main evening meal.
References
Teatime slot Wikipedia(Text) CC BY-SA