int t1, t2;
t1 = micros();
if (counts >=0 && counts <=80) b1 = 1;
else if(counts >=330 && counts <=410) b1 = 2;
else if(counts >=450 && counts <=530) b1 = 3;
else if(counts >=820 && counts <=1024) b1 = 4;
t2 = micros();
Of course there should be a "Serial.begin(115200);" command in your setup routine. You should mind that your code execution time depends on the value of "counts" (for counts = 60 only the first line is executed, for counts = 1000 all 4 if's are evaluated). To get the worst case you should ensure proper values for "counts".
I guess your code will take about 4 usec (in worst case), so you have to take into accout that the "micros()" commands take about 1usec each, so you will measure something like 6 usec.
If you want to improve your accuracy you can recopy your code several times between the two micros() commands and divide the final number accordingly. If you want to measure properly below 1us you need to set digital channels using port manipulation before and after your code and measure with an oscilloscope...