Labour Efficiency Variance

Question
XYZ Co is planning to make 120,000 units per period of a new product. The following standards have been set.
Per unit
Direct material A 1.2 kg at $11 per kg
Direct material B 4.7 kg at $6 per kg
Direct labour:
Operation 1 42 minutes
Operation 2 37 minutes
Operation 3 11 minutes

Overheads are absorbed at the rate of $30 per labour hour. All direct operatives are paid at the rate of $8 per hour. Attainable work hours are less than clock hours, so the 500 direct operatives have been budgeted for 400 hours each in the period.

Actual results for the period were:

Production 126,000 units
Direct labour cost $1.7m for 215,000 clock hours
Material A cost $1.65m for 150,000 kg
Material B cost $3.6m for 590,000 kg

Could you please explain “attainable work hours” and “clock hours” ?
It is correct if I said the standard hours we have been set is the target hours we should attain. However we know that in practice we will spend more time in production so we need budget more time and it is called “clock hours”?