How to calculate the time of turning on/off LEDs in four 8-bit shift registers with ATtiny2313-20U
For full transfer via bit-bang:

SBI on the 2313 takes 2 cycles per operation. At two operations per bit plus another to latch, that's 130 cycles.

For adjacent blink via bit-bang (e.g. 010101 &lt;=> 101010):

One operation for the set, one for the shift, one for the latch. 6 cycles.

For full transfer via USI:

7 cycles to get the byte into the USI via the simplified SPI master example in the datasheet plus the time required to actually send out the bits, all times 4, plus the latch.

38 cycles per byte using the high-speed SPI master example, times 4, plus the latch.

Conclusion:

At 1 / 20MHz = 50ns per cycle, much faster than your eye can see. Consider using one of the timers with an interrupt instead of banging it out manually.