How to configure logback to get nice logs of akka-http logRequest event

Question

As a result of the answer to this question I am able to get logRequest to log to a file called access.log.

I have

val routes =
      path("ping" ) {
        withLog(accessLog) {
          logRequest("ping", Logging.InfoLevel) {
            complete("pong")
          }
        }
      }

Part of my logback.xml configuration looks like

 <appender name="ACCESSLOG" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>log/access.log</file>
        <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
            <pattern>
                %d{yyyy-MM-dd HH:mm:ss} %msg%n
            </pattern>
        </encoder>
        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            <fileNamePattern>log/access-%d{yyyy-MM-dd}.%i.log</fileNamePattern>
            <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
                <maxFileSize>64 MB</maxFileSize>
            </timeBasedFileNamingAndTriggeringPolicy>
        </rollingPolicy>
    </appender>

And the resulting entry in the log file looks like

2019-02-06 16:51:04 ping: HttpRequest(HttpMethod(GET),http://localhost:8080/ping,List(Host: localhost:8080, Connection: keep-alive, Cache-Control: max-age=0, Upgrade-Insecure-Requests: 1, User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36, Accept: text/html, application/xhtml+xml, application/xml;q=0.9, image/webp, image/apng, */*;q=0.8, Accept-Encoding: gzip, deflate, br, Accept-Language: en-GB, en-US;q=0.9, en;q=0.8, Cookie: xxx, Timeout-Access: <function1>),HttpEntity.Strict(none/none,ByteString()),HttpProtocol(HTTP/1.1))

What can I do to get my log entries to look something like

2019-02-06 16:51:04 GET /ping <time_taken>