• день добрый.

    как будет правильнее?

    на выходных - at the weekend or at the weekends?
    по четвергам - on Thursday or on Thursdays?

  • Weekend
    noun [ C ] UK ​ /ˌwiːkˈend/ US ​ /ˈwiːk.end/

    A1 Saturday and Sunday, or Friday evening until Sunday night; the part of the week in which many people living in the West do not go to work:
    This/Next weekend we're going to see some friends.
    I have a lot of homework to do over the weekend.
    He spent the weekend fishing with his brother.
    uk Do you have anything planned for the weekend?

    a trip or a visit at a weekend:
    How much would a weekend for two in New York cost?
    They own a weekend retreat in the country.
    at the weekend uk us on the weekend
    ​Внимание:. в выходные, на выходные ---конкретные.
    on Saturday or Sunday, or on both Saturday and Sunday:
    What did you do at the weekend?
    We go out once in a while after work and at the weekend.
    at weekends uk us on (the) weekends
    Внимание: по выходным (часто, обычно)

    usually or often between Friday evening and Sunday night, or on Saturdays and Sundays:
    They go windsurfing at weekends.

    то же с днями недели
    On Sunday---в воскресенье, on Sundays --по воскресеньям