In the timeline, move the date from the side to as a header above the entry and have one date header for all the entries in a day. The former and latter would give significantly more room for the text of the entries on mobile. These aren't as important for the larger screen devices (computers and tablets) since there's much more screen real estate but for consistency and saving some extra space, I don't see why not to implement it there too.
Diarium version: 2.7.9.0 & 2.7.8
Operating system: Windows & iOS