sync_timeout

I am fairly new to Makefiles and the like, so this may be a stupid question, but how do I set the value of sync_timeout in src/systems/manager.cc when making without having to hardcode a new value for it? ps-lite is being built as a dep in my build for wormhole, and I'm wondering what the most straightforward way to set the value of sync_timeout would be from a command line make call?