Inspired by this article:
A QR generation library was ported to the Arduino UNO and Seeed LCD touchscreen platform. Originally the generation time was 6 seconds, making the display of seconds impossible.
As @ch00ftech suggested, eliminating the search for the optimal QR mask and instead applying a fixed mask, drops the generation time to less than one second.
Using a fast TFT display library by @Xark allows seconds to be displayed. This library was modified to comply with the calling convention for @seeedstudio libraries, making it a drop in replacement in an existing sketch. By changing a compiler directive, this library can also control an @adafruit LCD.
As a further optimization, the last QR code generated is stored in a bitmap so only the pixels that change are painted.