replication timeout

I have two Dovecot mail servers that replicate to each other. Sometimes there are delays in the synchronization, and I notice that the mail log has entries like this:

Error: dsync(spokane): I/O has stalled, no activity for 600 seconds (last sent=mailbox, last recv=mailbox_state)

Five minutes seems like a long time to sit there waiting with nothing happening. Is there a way to reduce this timeout so that I don't have so many replicaton connections just sitting around doing nothing?

(Of course, a way to prevent the I/O stalls would be great too, but with my limited upload bandwidth, they may be unavoidable.)

Andy