It's more like when they're finished they leave and if they are an hour early or late is not relevant as long as the duties are done.

For example you say I need this restaurant cleaned during closing hours which are between 1am-9am and I want you to start at 1am every day! Your cleaners show up at 3am one day and get all the work done in six hours.

The next day they talk and drink coffee and leave the site three or four times to go take naps but the restaurant is still clean at 9am

Employees you could repremand in both situations but if they're contractors not so much. As long as the job is done within the ranges established in the contract they can do it however they want. If they can clean the whole restaurant in 10 minutes by bring in a crew of 30 men and paying them each 50 cents that's their prerogative