Assist feeding should be done as a last result and when everything else has failed and this decision is usually based on the overall look of the animals, it can take several weeks for an hatchling to start eating on it's own.

Here is what I used to do when starting everything on rats (I now start everything on mice now)

I would offer food 48 hours after the first shed, live rat crawler, following week live crawler again, same thing for the third meal, if by the third meal I still had refusal those animals would be offered live hopper mice.

Here are a few other thing that help

6 quarts or V18 tubs are rather small so make sure the hot side is not to hot, in my experience they do better if the hot side is no higher than 88/89.

Use aspen for bedding this allows them to bury themselves offering a sense of security.

If you keep having issues provide a 6 inches plastic flower pot saucer as an hide.

Use crumble newspaper in the tub to "junk" it up.

Use the brown paper bag trick

and most importantly do not mess with them, no handling, no checking on them 10 times a day etc.

Again a week is NOTHING