This message is typically raised because LonMaker is trying to update devices on the network.
If the delay is long, it can be because there are a lot of devices that needs updating and/or LonMaker can not communicate with them.
To see if this message is indeed due because LonMaker is trying to update devices in the background, you can try setting the Update Interval property to 0. This can be done in LonMaker by going to the LonMaker menu->Network properties->Timing. Setting the UpdateInterval to 0 will prevent LonMaker from updating devices in the background.
Please note that this setting is not usually recommended. You should make sure that all your devices are up-to-date and then reset this property to the default value.