What is the page size for every delta query?
https://developer.microsoft.com/en-us/graph/docs/concepts/delta_query_users https://developer.microsoft.com/en-us/graph/docs/concepts/delta_query_groups
My understanding is the $top doesn't work with delta query on users and groups. So we cannot set a custom page size.
TL;DR: For delta queries page size is not fixed/guaranteed. There's Prefer: odata.maxpagesize=X parameter but it doesn't work for all queries.
If you try to reproduce this situation in Graph Explorer using the following:
https://graph.microsoft.com/v1.0/me/calendarView/delta?startDateTime=2010-01-01 00:00:00&endDateTime=2020-01-01 00:00:00&$top=5
It'll give you the following error:
The '$top' parameter is not supported with change tracking over the 'CalendarView' resource as page size cannot be guaranteed. Express page size preferences using the Prefer: odata.maxpagesize= header instead.
As stated in this error page size is not guaranteed. However, by adding additional header
Prefer: odata.maxpagesize=10
you will be able to see that only 10 results are returned.
One remark - this param is not supported for some of the resources (also for the ones you asked about - user and group).
To see if the delta query for the other resource is supported, go to this page, choose the API and go to Request headers paragraph in its documentation. If you find header with odata.maxpagesize={x}. Optional. in the description - it's supported.
As for today (July '18) the following APIs support odata.maxpagesize param: event, mailFolder, message, contactFolder, contact and the following don't support it: group, user, driveItem, plannerUser.
Feel free to play with Graph Explorer as it might be very helpful in troubleshooting.