The correct answer is: C. Either I or II is implicit.
The statement says that the programme will start at 6 p.m. but you can come there up to 7 p.m. or so and still there is no problem. This means that the programme will continue for at least an hour after 6 p.m., and that it is not essential to arrive at the start of the programme.
Assumption I is that the programme will continue even after 7 p.m. This is a reasonable assumption, given that the statement says that you can come there up to 7 p.m. or so and still there is no problem.
Assumption II is that the programme may not even start by that time. This is also a reasonable assumption, given that the statement does not say that the programme will definitely start at 6 p.m.
Therefore, either assumption I or assumption II is implicit in the statement.