The infinite scrolling is only supported for timelines generated automatically (scale !== "Manual"). However, it's possible to adjust the generated time cells using onIncludeTimeCell to achieve the same result:
dp.onIncludeTimeCell = function(args) {
args.cell.start = args.cell.start.addHours(12);
args.cell.end = args.cell.end.addHours(12);
};
This will work fine with infinite scrolling.
The latest sandbox build (2020.2.4515) generates correct time header groups for a timeline that was shifted this way.