Around 8.5 hours, of which LL was present for around 5(if she started at around 7.30) I wouldn't say dozens had access, as the insulin and TPN bags were kept in a locked fridge so it would need to be somebody who had asked for the key and had reason to be accessing the fridge. Not sure what other medications were in there but no other baby was on TPN and no baby was receiving insulin.
The jury don't have to work out how she may have done it though. Although the prosecution seem to think she injected it into the first(or possibly only) TPN cotside. Johnson said "To give Child F insulin someone would've had to access the locked fridge, use a needle and syringe to remove some insulin, or, if they didn't do it that way, go to the cotside and inject the insulin directly into the infant through the intravenous system, intramuscular injection, or - and this is what we say happened - via the TPN bag."
JMO