Your question isn’t clear, you say time remaining is zero when on full charge?
The time remaining display is for discharging, not charging, so it won’t display anything while under charge.
If guimods is doing something else to that readout, I can’t say as it isn’t a mod that I have used. You can check this by using victron connect to view the shunt data.
The battery monitor estimates how long the battery can support the present load. This is the “time-to-go” readout and is the actual time left until the battery is discharged to the set “discharge floor”.