They seem to vary by a few weeks .. My main crop outdoors were all started indoors in my polly tunnel. These have been heavily producing for about 4 weeks now.
Whenever I transplant them outdoors I always put a couple of spare beans around each plant just in case the main one fails.
The spares are well on their way up the canes now and will be producing within a week or so.
Other allotment holders around me have been complaining about how late they are this year ... but they don't start them off indoors.
I maintain if you start them early and get it wrong, then you can always fall back on your spare bean plan.