Best way to turn boolean tag value high every 5 seconds?

[zacht]

Smart people suggest that it's good practice not to write to one tag from two sources (Ignition and PLC). Example:

Heartbeat script having effects system wide

Eeek! No. Don’t write from two directions. PLC should count and roll over. The low word of a PLC clock is fine. Ignition should count and roll over in its own timer event, writing to the appropriate OPC tag. Or write the low bits of Ignition’s millisecond time to the OPC tag. It isn’t important what the value is, just that it changes regularly. Neither the OP nor @jdrichards70 shared their actual scripts, so there’s no telling what the real problem is. Non-blocking writes should be use…

I know that doesn't answer your question, but I think you could benefit from searching "handshake" on the forum and seeing how others have implemented.