You could run the JA server in a named screen session, set up an hourly cronjob and pipe to stdin of that screen (i.e. invoke screen with the -X switch)
Apart from that, I'm not sure what can be done with JA+
With JA++, you could quite easily set up a Lua plugin to broadcast a message every x seconds, among many other things.
EDIT: I suppose you could also rely on an external RCON method, i.e. running a php script or java app to send an rcon packet on a timer. I think JAWA currently does something like that. @@SiLink?