An employment contract is seen as subject to a General or a Normative Work Agreement, (like the one to which Kri linked, above) which has typically been agreed between the professional body of a certain type of employers (e.g. the entertainment industry, or the building branch, etc.) and the representatives of the employees (usually a trade union), or individual.
If the type of work falls under a General or a Normative Work Agreement ,
then the terms and conditions of that agreement apply. This is so even if they are not expressly mentioned in the work contract.
If the contract is individual ,
then the date of payment of the wages is either according to OR Art. 323 1, or according to what has been arranged in the individual contract, which can be written or verbal.
Moreover, an individual contract can even circumvent the General or a Normative Work Agreement, simply by stating that both parties agree to the terms as specified in the individual contract.
https://www.fedlex.admin.ch/eli/cc/2.../lvl_C/lvl_I_I
1 Unless shorter periods or other payment terms have been agreed or are customary and unless otherwise provided by standard employment contract or collective employment contract, the salary is paid to the employee at the end of each month.
Therefore, it is perfectly legal for an employer to state that they process their timesheets and add up the hours only after the close of the month, and for them to pay the employer a few days' later. Some small employers much prefer this to trying to "break" the month on a day other than the last calendar day, because it streamlines their simple bookkeeping.
Having said that, there's a nice little addition in paragraph 4 of the same article: 4 If an employee is in hardship and requests an advance against salary due for work already performed, the employer must advance such sum as may equitably be expected of him.