Hi Chinnated, I don't know whether the Python SDK itself has the feature for schedule or not but you can do it with schedule module like below:
schedule.every().day.at("18:00").do(send_messages)
Note that the time the job will be processed depends on the localtime of the runtime environment.
Scheduling feature is not supported in line-bot-sdk-python. but you can implement a scheduled message with pure python library like https://github.com/dbader/schedule.