When the X-axis is set to style ‘Time’ or ‘Date,Time’ the time portion of the axis labels may be formatted with a simple picture format such as:

chSet 'tpic' 'HH:mm-ss'

To label the tickmarks ‘14:12-34’ and so on.

The time specification in detail
The following table is taken from the Microsoft documentation for the GetTimeFormat API call, and is common to all Windows applications which use it:

Picture	Meaning
h	Hours with no leading zero for single-digit hours; 12-hour clock
hh	Hours with leading zero for single-digit hours; 12-hour clock
H	Hours with no leading zero for single-digit hours; 24-hour clock
HH	Hours with leading zero for single-digit hours; 24-hour clock
m	Minutes with no leading zero for single-digit minutes
mm	Minutes with leading zero for single-digit minutes
s	Seconds with no leading zero for single-digit seconds
ss	Seconds with leading zero for single-digit seconds
t	One character time marker string, such as A or P
tt	Multicharacter time marker string, such as AM or PM

If you use spaces to separate the elements in the format string, these spaces will appear in the same location in the output string. The letters must be in uppercase or lowercase as shown (for example, “ss”, not “SS”). Characters in the format string that are enclosed in single quotation marks will appear in the same location and unchanged in the output string.

See also ...
DateFormat – picture specification
Locale – for formatted dates or times