Edit any time block. Tap any time block in the timeline to edit it. You will get an editor below the block that lets you (a) assign a different timer (by tapping the name of the current timer), (b) change the start and end times of that block by tapping on the "<" and ">" buttons, and (c) add or edit the notes.

Swipe to move to other blocks. When the time block editor is showing, you can swipe the editor left and right to edit other blocks on the timeline, or tap on a different block to edit it.

Assign/edit unassigned blocks. You can go back to any part of the day that is blank on the timeline by tapping in the approximate place where you want to assign time. You will see a list of your timers, and you can tap one to assign that timer to the selected block. Then you will see the time block editor so you can edit that block as described in #1 above.

Split a block. You can split a block in two by tapping on it, then tapping on the Split button. The time block editor will then be positioned under the first half of the split block so you can assign it to a different timer, change start and end times, etc. You can swipe the editor to the right to edit the second half of the split block in the same way.

"Took Break." You can insert an unassigned area within a block by tapping on that block, then tapping on the Took Break button. You can then tap on either of the resulting assigned blocks or the inserted unassigned block to edit them as needed. The amount of time that is inserted is based on your rounding rule settings.

Delete a block. You can delete a time block by tapping on the block and tapping on the Delete button. 

Change total time of a timer. You can also always change the total time under any timer for the day by tapping on the colored total time box at the left side of the timer.