I was just about to reset everything back to default...
Thank you @hnyman and @Borromini. The command revealed a wrong line in the config file and the example of hnyman guided much better than the OpenWRT wiki, which I believe has room for improvement.
I changed /etc/config/system to
config system
option hostname 'OpenWrt'
option timezone 'CET-1CEST,M3.5.0,M10.5.0/3'
option zonename 'Europe/Paris'
......
and the result is

Cheers
Oscar