Manually delete time machine backups

I want to manually delete some time machine backups. But *not the oldest ones* that would be automatically deleted next time I use Time Machine. In other words, I want to preserve the oldest backups and delete some recent hourly ones. These were created overnight, when there were no changes, so they're unnecessary.

I followed advice in Apple Support but it is incomplete. Here's what I did so far:

1. Click the Time Machine icon  in the menu bar, then choose Enter Time Machine.
2. Use the arrows and the timeline on the right side of your screen to browse the backups Time Machine created.
3. Select the item you want to delete, then click the Action pop-up menu  and choose Delete All Backups of [item name].

I deleted two complete backups from a specific date. For example, all of "Saturday, July 20, 2019 at 3:09pm".

However - since that moment, eight hours ago, both of these deleted backups are still showing in Time Machine, with the title: "Waiting: Saturday, July 20, 2019 at 3:09pm"

I can't find information on how to get past this limbo. Unable to delete these backups, and thus unable to use Time Machine for my next backup (because I don't want to automatically delete the oldest backup).

I'm using 10.13.6 High Sierra on a 2017 13" MacBook Air. Time Machine is on a 4TB LaCie external drive, format Mac OS Extended (Journaled), about a year old.

Thanks - Fran