best you can do is split the time format to put the am/pm on a new line
short of rewriting the entire qml for the clock, a new line is the next best thing.
from my notes:
Configure Digital Clock lets you set the format and font
Appearance
- show date
- date format custom
ddd M/d yyyy
- font
48pt Bernound
#to move the AM/PM of the 12hr digital clock to a new line, edit this .qml
#~/.local/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/DigitalClock.qml
/usr/share/plasma/plasmoids/org.kde.plasma.digitalclock/contents/ui/DigitalClock.qml
#find the function timeFormatCorrection (at line ~651) and for the *if* statement change
result += " " + amPm;
to
result += "\n" + amPm; // puts amPm on new line for larger font in vertical panels
#to change the clock color search the .qml for "id: timeLabel" and add this line under it
color: "#69ffff"
#to change the date color search the .qml for "id: dateLabel" and add this line under it
color: "#cdffff"