As the unchanged blink sketch blinks with 8.4 seconds, I think my assumption is right. The clock of the Attiny is running 8 times slower, than the code thinks.
When you have installed the Attiny core, there should be a menu entry for the clock frequency. Most likely the standard is 8MHz. But having 8MHz set does not mean, that the Attiny is using 8MHz. To ...
The code you wrote should work as expected. If it doesn't, I suspect
there is something broken in the Arduino core you are using. However,
such a trivial task can very easily be programmed in plain C, at the
#define F_CPU 1000000 // 1 MHz
DDRB |= _BV(PB3); // PB3 ...