Definitely Pulisa. The govt can't afford to dawdle this time round, as I already mentioned upthread, they would be committing political suicide by doing so, especially as they screwed up over Delta earlier this year where they added India to our 'red list' too late and Delta had already been let loose in this country by then.
For once, even the Shadow Home Secretary has welcomed the swift action and 'safety first' approach by the govt, where opposition MPs would usually otherwise be dishing out criticism (justified or not).
My only concern is that this new variant will inevitably still make it to our shores indirectly via other countries of whom are still lax on flights to and from SA (and other places where this new variant is also known to exist), and also testing and quarantine arrangements for those returning from SA.
I suppose as always, only time will tell.
ETA, Other countries/nations are now also discussing restrictions on travel to and from SA, e.g, mainland Europe, Australia and Singapore.