def parse_hhmm_field_from_form(data_dict, key_root):
    """ Extracts and parses the hours and minutes inputs to create a
    parseable time of day string in HH:MM format. These times are
    displayed as two select fields designated with a name (key_root)
    and _hours or _minutes suffix.

    Parameters
    ----------
    data_dict: dict
        Dictionary of posted form data

    key_root: string
        The shared part of the name attribute of the inputs to parse.
        e.g. 'issue_time' will parse and concatenate 'issue_time_hours'
        and 'issue_time_minutes'

    Returns
    -------
    string
        The time value in HH:MM format.
    """
    hours = int(data_dict[f'{key_root}_hours'])
    minutes = int(data_dict[f'{key_root}_minutes'])
    return f'{hours:02d}:{minutes:02d}'