The phrase "dreaded day" refers to a day that someone feels fearful or anxious about because they anticipate something bad or unpleasant happening. Full definition
I also dread the day when he will be ready to sleep in his own bed. (attachmentparenting.org)
Well, it's basically one of my most dreaded days of the week, when — you guessed it — I sit in front of the computer all day long. (halfbakedharvest.com)
I laugh as I read this but I also dread the day. (thirstiesbaby.com)