What should I do

I am going out of town April 26-29th. I am currently off birth control but I am going to be getting back on it after being off of it for about a month. Before I had taken it for about six months. I will be taking the same birth control. According to the eve app which is usually close to my starting date, my period will start the 19th. My period usually lasts about 7 days. So id basically be done by the time my trip is. However, i’m worried that eve will not be correct and i’ll be on my period during my trip. I’m going to a music festival and this will be hard because it’s all day and i try not to use portapotties as much as i can. So my question is, if i take my birth control starting tomorrow (it has 24 active pills) would i not get my period until the pack is finished? Usually on this pill i get it the first day of my next pack. Or should i just let this upcoming period happen as planned and start my birth control then?