General Caster - lags in the timeline

I have a timeline column, and a numerical lags column and I’m looking for something that will make the timeline move according to the number entered in the lags.
I tried to use the ability of general caster (from timeline to timeline) by the formula -

CONCATENATE(TEXT(DATEVALUE(LEFT({item’s Timeline}, 10)) + {item’s Lags} , “YYYY-MM-DD”), “+”, TEXT(DATEVALUE(RIGHT({item’s Timeline}, 10)) + {item’s Lags}, “YYYY-MM-DD”))

But I encountered 2 problems:

  1. I couldn’t implement the formula on the timeline itself, meaning the formula only works if I add another timeline, but I’m not interested in 2 separate columns but only one.
  2. I didn’t find a way for the days to be added according to the working days. Currently it adds days but the date is not updated according to the working days.
    I need your help to solve these problems . Thanks