Microsoft just released Windows 10 Insider build 17083, and as has been the norm lately, it's chock full of new goodness, including news of some Timeline improvements, set in motion by Windows Insider user feedback.
One of the most requested changes was for an ability to make it easier to delete multiple activities from the Timeline. In this new build, you'll now be able to "delete everything from a given hour or day from the context menu":
When you are in the default view, you will see a new “clear all from day” option when right-clicking on an activity. If you clicked “see all” to see activities for just one day, this option changes to allow you to “clear all from hour” instead. Because this option can clear a lot of activities at once, we will ask you to confirm this choice before deleting the activities.
In addition, and in keeping with this build's focus on privacy, you'll now be able to have access to more granular control of the privacy of activities:
A new setting allows you to sync your activities to the cloud for a seamless cross-device experience. You can enable “Let Windows sync my activities from this PC to the cloud” in the settings app, or you can enable it via an option provided at the bottom of Timeline. Until new users enable this setting, Timeline will only show four days of activities. (If you are upgrading from an earlier WIP flight, you may not see this option as the setting is already enabled.)