Practise tightenings

So

36 weeks and 2 days! Had a midwife appointment today and she was feeling my tummy and said I was having “practise tightenings” since then I’ve noticed all afternoon it’s been going hard and I’ve been having mild cramps on and off really regularly. ... Is this an early sign of labour? Or can this last for weeks before actual labour happens? (Sorry, first time mum!)