Separation Methods and Minima: DGCA Air Regulations questions

An aircraft is maintaining FL 150 within airspace class D. Another aircraft below at FL 140 is receiving a clearance to descend to FL 70. It is severe turbulence in the area. When is the earliest that a clearance to descend to FL 140 or below can be expected?

The longitudinal separation minima between aircraft departed from the same aerodrome and following the same track, and the preceding aircraft is maintaining a true airspeed of 20kt or more faster than the succeeding aircraft, is:

The longitudinal separation minima based on time between aircraft at same cruising level where navigation aids permit frequent determination of position and speed and the preceding aircraft is maintaining a true airspeed of 40kt or more faster than the succeeding aircraft, is:

The longitudinal separation minima based on time between aircraft at same cruising level where navigation aids permit frequent determination of position and speed and the preceding aircraft is maintaining a true airspeed of 20kt or more faster than the succeeding aircraft, is:

The longitudinal separation minima based on time between aircraft at same cruising level where navigation aids permit frequent determination of position and speed, is: