Completly lost with how to parse date

[Elastoc]

Hello,

I'm trying for several hours to parse a logfile and i'm stuck with parsing dates. I have a very hard time understanding how it works. Is there an example somewhere with unusual timestamps?

My log is like this :

XXX.XXX.XXX.XXX - - [31/May/2019:07:10:01 +0200] "GET -url- HTTP/1.1" 200 446 413 5 "-URL-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:67.0) Gecko/20100101 Firefox/67.0" -URL-

`
Filters in my ".conf" file :

filter {
        grok {
                match => { "message" => "^%{IP:host_ip} - - \[%{TIMESTAMP_ISO8601:logtime}\]" }
        }
        date {
                locale => "fr"
                match => [ "logtime" , "dd/MMM/yyyy:HH:mm:ss Z" ]
                timezone => "Europe/Paris"
                target => "logtime"
        }
}

When i get rid of the timestamp thing, it parse the IP address but not with it...
What can i do to make it work? Should i mutate the timestamp to get it with "-" and not "/"?

[Elastoc]

I really was searching for long but just found how to

            match => { "message" => "^%{IP:host_ip} - - \[%{HTTPDATE:logtime}\]" }

But i still wonder how to do with non predefined patterns...