There currently isn’t a way to not use time on the timeline, however if it is only page numbers that you are wanting to track, then you could still use the date on a timeline to represent this, even though that is not what is intended.
If you open Timeline Settings, and set the maximum precision to be “Year”, then your dates will only have years in them (eg .2023, 2022 etc).
Then your dates will all be in the format of a single number, and therefore could represent page numbers instead. (Year 1 could be Page 1, a duration of 2 years would be 2 pages etc.) There isn’t a way to change the text to reflect this, but it would still display like you are wanting on the timeline, especially if you adjust the zoom levels so that you don’t zoom past years to start showing month intervals etc. on the timeline.