Universal credit help...

So please so judging but iv had to leave work due to childcare issues (baby is 8months) we tried to make it work after going back from maternity leave but it just wasn't working for both me and the employer. Im abso gutted about this as iv worked since i was 16 ( now 29) iv tried searching for jobs that could work around childcare etc but its been impossible to find any and i suppose with the curre t situation doesnt help. Anyway I'm going to have to apply for u.c. I am a single parent and currently on the old working tax scheme. I received my last payment from work yesterday as we work a week In hand along side my holiday pay id accumulated. Now when should I pay for uc? As iv heard i should leave it a few days after receiving last pay as they would take it into account and I wouldn't get a payment from them. Now I'm not trying to fraud the system its just so iv got money aside to pay bills, my rent and be able to provide for my 2 children untill my uc payment comes in as It can take up to 5weeks and I dont want to be left stuck if that makes sence. This is just going to be a short time solution and hopefully things will change regarding childcare/covid by the middle of next year and I can then return to work. I hate NOT working its driving me crackers.