How long can a Braxton Hicks last?

[stowsettler]

I'm 37+3 and getting the occasional odd sensation. The top of my bump just seems to suddenly be as hard as a rock, to the point of being mildly painful / uncomfortable. I don't notice the hardness coming on, and it seems to last at least 5 minutes. Could this be BH?

Very likely. BHs can last for a short time or in my case an hour or more (not comfortable!).
Main distinction between BH and proper contractions is the irregularity and lack of increasing intensity. BH do border on painful, I'm having one now that's pretty horrible.
Mine started at about 25 weeks with dc1 and got v uncomfortable by 36-7 weeks, DS was still 13 days overdue though! This time started at 16 weeks (!) and v uncomfortable fom 26 weeks. 29 weeks now and no sign of it shifting baby thank goodness.
Good luck

Thanks mincepies. Although I'm not to enamoured at the prospect of going 13 days overdue!!! But an hour?!?!?!? Poor you, hope they're not all that bad and that DC2 is on time for you.

I have had them a lot during this PG. Never had them (or noticed them) with DC1. I have had some very uncomfortable ones which have caused me to stop what doing and have to lie down with lower back ache and pressure underneath and lasted a few mins and come and gone every 20 mins. I have also had the odd one with no discomfort other than tightening. I asked my MW and she said that once you have been getting tightenings with pain regularly every 10 mins for up to 1-2 hours then call hospital as this is labour and not BH. BH will usually not be regular and will stop after a while but labour will keep coming and getting stronger.

Mincepies that is reassuring as I am exactly the same as you. From 26 weeks in first pregnancy and from 16 weeks in this one. I am so uncomfortable. I seem to have them throughout the day and night constantly now I am 33 weeks. Its all normal though and yes they can be on the verge of being painful but not any indication of preterm labour. IME labour feels a lot different to BH.