Odata.Nextlink is provided only when there are more number of records you get as a response. There is a concept of paging where the api's have their own default number of records per page. Here since you are using getScheduler, it gives you a response of different schedules of users or distributed list or resources you asked in the payload. Top is used when you want data of a HTTP call in a single page. It can accept values between 1 and 999. Please check this document.
Also try with 30 accounts and you should be able to see 20 account schedules per page.