Such a hard question to answer...too early and I think it’s really hard to just relax, move around, eat and sleep as you need to, increasing the risk of interventions etc...too late and there’s the risk of giving birth in the car park!
I have had 3 SVDs. No 1, definitely went in too early, although baby was back to back and it was pain management that brought us in. I just wast getting any relief between contractions. But that meant being flat on my back with an epidural and a slower progressing labour, worn out baby then forceps. No2 I stayed at home with regular contractions using hypnobirthing and TENS. Nothing much changed all day until I started to feel really irritable and went in. This was basically transition and a bit too late probably! Born within 30 minutes of arriving at hospital with gas and air only. No3 was born last week and I tried to find the balance between 1 and 2 but ended up in pretty much the same boat as No2. So glad we got there in time as this one had the cord around her neck several times and her hand by her face making delivery a bit complicated; she needed a little resuscitation, I lost a lot of blood. A reminder of the advantages of hospital birth even when complications are not expected.
For me, all three started with a bit of a show and gradually escalating contractions. No waters leaking or breaking until delivering. I also seemed to get a long plateau of 1 contraction per 10 minutes before a sudden escalation in just the last hour, accompanied by a dramatic change in my mood.
I think everyone is different and the best thing is to call your labour suite with updates, so they can hear how you are doing, be prepared for your arrival and give advice. Your partner can do this, as well as recording contractions on an app, if you want to zone out and sleep on and off through the earlier stages.