'increasingly earlier' is correct and usable in written English.
It is commonly used to describe a trend of something happening at an earlier and earlier time. For example, "People have been reported to wake up increasingly earlier as winter approaches."
Survival of premature infants born at increasingly earlier stages of gestation has made the prevention of lung injury increasingly challenging.
However, competition among retailers and an oversaturation of deals mean ads are leaked increasingly earlier, discounts have become less competitive, and Black Friday has become more like Black November.
We showed that genes without introns, genes with only large introns and genes with minimal introns have increasingly earlier replication time and more open chromatin structure.
However, these changes occurred at an increasingly earlier age with higher dieldrin treatment levels.
Reconstruction, rehabilitation and development initiatives start increasingly earlier after crisis, unleashing tensions between development and humanitarian paradigms.
Owing to increasingly earlier detection and improving therapies, the life expectancy of people with cancer has been increasing.
The trains became crowded at an increasingly early hour.
An increasingly early Arctic spring could increase plant growth by up to 25%.
Today, educational technology boosters believe computer games (the classroom euphemism for video games) should be part of classroom lessons at increasingly early ages.
Increasingly early exits for middle-aged performers merely reinforce the absence of grown-up themes in a format once founded on them.
At a time when youngsters adopt professional habits and attitudes increasingly early, at a time when agents, sponsors and federations are particularly focused on finding and funding the next big thing, the extreme youth movement has hit a roadblock.
