IMHO, two or three rolled on fill coats in quick succession, applied as soon as reach green stage, will be safest. You will have a chemical bond between coats. You can wait until frayed edges are sandable before fill coats but then you have to get all the amine blush off if there is any, and rely on a good sanding for bonding between coats. This may not be so easy on unfilled glass surface. I don't think there will be much difference in appearance after finishing.