The default vhost doesn’t use the sethandler directive AFAIK.
For all virtualhosts you need a custom template to make the changes persistent.
Create the custom template dir:
mkdir -p /etc/e-smith/templates-custom/httpd/vhost-extra
Create /etc/e-smith/templates-custom/httpd/vhost-extra/14timeout
with following content:
#
# 14timeout
#
TimeOut 300
ProxyTimeout 300
Apply the configuration:
signal-event nethserver-httpd-virtualhosts-update
I recommend to update to 7.7