I wouldn’t bother spaning them if eating ad lib creep...just get them killedIf taking significant amounts of creep you could wean at 8 weeks.
Early lambs won't grow much after 6 weeks without creep as milk drops off and grass is poor. If the grass is there (later lambing) fair enough. But there won't be much about on march in most places. Creep will get them away far faster.We get first lambs away fat at 12 weeks which is late June. Straight off mothers, no creep.
Yours should be eating plenty grass by mid-April and growing without creep. I wouldn't wean them if going fat as they will just bleat for 3 days. Occasional mastitis here but not worth bringing them in even if that would prevent it as I am not sure it does.