import re


def get_ospf_spf_start_time(log):
    """
    Get OSPF spf start time in log 'Jun 12 03:40:19.068983 Starting full SPF for topology default' 

    Args:
        log ('str'): log string

    Returns:
        date time ('str')  
    """
    # Jun 12 03:40:19.068983 Starting full SPF for topology default
    p_start = (
        '(?P<date>\S+\s+\d+) (?P<start_time>\d+\:\d+\:\d+\.\d+) Starting full SPF for topology default'
    )     
    m = re.match(p_start, log)
    
    try:
        if m:
            group = m.groupdict()
            start_time = group['start_time']
            return start_time
    except KeyError as e:
        raise KeyError(f"Key issue with exception: {str(e)}") from e