More crop problems

Some of my 10 day released ex-batts have large crops this morning (they have gone down from lat night, but are still distended) and I am at work worrying about them.  It is easier to see on some as they have bald chests, I can't tell on the ones with feathers.
-They are in a outdoor run and they have oyster shell but no grit (as that was what I was sold when I asked for grit).  If I buy some grit could that may make a difference?
-I fed them on some long grass on saturday, just before I realised I shouldn't.  If it is this that has caused the problem is there a chance it still may pass

At a risk of people having to repeat the good advice already on the forum.  How quickly does this problem get serious for the hens?  They are all happy and eating at the moment.   They are harder to catch now they are more confident.  My plan is to feel their crops in the morning and then start worrying!  I don't think I can do the olive oil/mineral oil/massage as I am on my own.  I am quite happy to take them to the vet, should I wait and see how they are on monday or panic earlier?
Again, I am very grateful for any advice.

Thank you so much, I am reassured and calm again now and have bought some grit and cider vinegar.
Many thanks.