// Created on savesnippets.com · https://savesnippets.com/FOK42BBIZ2dPcU
<?php
function recentFiles(string $root, int $days): array {
    $cutoff = time() - $days * 86400;
    $out    = [];
    $it = new RecursiveIteratorIterator(
        new RecursiveDirectoryIterator($root, FilesystemIterator::SKIP_DOTS)
    );
    foreach ($it as $file) {
        if ($file->isFile() && $file->getMTime() >= $cutoff) {
            $out[] = $file->getPathname();
        }
    }
    return $out;
}

print_r(recentFiles('/var/www', 1));  // everything touched in the last 24h