Map timestamp label has unstable width

[corviday]

The map timestamp controls use a central react-bootstrap Button as a label to display which timestamp is currently being shown. The width of this button changes based on things like month name length, which causes the positions of the controls on either sides to jump around a bit while clicking through timestamps. A user has expressed annoyance at "missing" a button that moved between clicks. It seems possible to set a consistent width on the central button to prevent this.

[rod-glover]

Seconded