Origin149 fix start time examples2

[javiarrobas]

Fixes #149.

[javiarrobas]

@IamAniket12 FYI: I'm sorry but I had to revert the edits to have just one argument for start_time in the environment. The reason is that if we remove the random_start_time_variable, whenever we restart the episode here we assign a value to start_time which is thus not None anymore. This makes further resets of the environment not to find a random start time but always start by the same one.

[IamAniket12]

@javiarrobas I believe we can manage this edge case in the script without explicitly passing the random_start_time variable. If you think it's a good idea, let me know and I'll give it a try.