Hi.
Whenever you compile text that is not assigned a style, it doesn’t matter how it looks in the editor, it will end up — unless you compile “as-is” — formatted as specified in the section layout it compiles through :
To set specific formatting to parts of your text (not for the whole, but rather for parts that differ in formatting from the body text) use a style. (Your dates, in this case.)
Whatever has a style applied will compile as per that style rather than as per the layout’s formatting shown above.
That style will be listed in your epub’s CSS stylesheet, telling the ereader how these bits should be formatted.
. . . . . . . .
[EDIT] I mistakenly worked on a screenshot from a RTF setup, some details are slightly different when compiling to epub, but other than the looks of things, the idea is the same.