I had a similar issue with outlook, by default I now set outlook server timeout to 3 minutes, under advanced settings.
this is one thing, as clamd will need to download the whole file and then scan it and finally give a result, it could take time when file are larger
also to avoid delay because of 24 update daily you can do this
# config setprop clamav Checks 2
# service freshclam restart
where it will only update the db twice daily.
the default from clamav is 12, SME default is 24, i.e. once hourly at least + multiple tries if it fails.