generate weekly shift with two days off contraints

I want to randomly generate a 8 hours shift for worker.

Start from 0 to 24*7+8(next monday's 8am). Each day has a start time and end time.

(0,0) if off.

the output should look like this:

[[  0   0]
 [ 29  37]
 [ 60  68]
 [ 80  88]
 [  0   0]
 [121 129]
 [165 173]]

Shift can be overnight: eg, 23--31 for 1st day.

There must be a 12 hours gap between shifts. from example above: if the 2nd day is not off, then 2nd day shift starts from 32.

if 3rd day off, end time of 2nd will be 48-1. so wiggle room for 2nd is [32,47]

This is the code I wrote:

import numpy as np
def shift8h():

shift = np.zeros((7, shift_start_end), dtype=int)
twodaysoff = np.sort(np.random.choice(range(7), off_days_8h, replace=False)) # random 2 dif number
#twodaysoff=[0,4] # twodaysoff=[1,6] # wodaysoff=[0,1] # twodaysoff=[1,2]

work_days = np.setdiff1d(days, twodaysoff) # 5 work days

for i in work_days:
    for j in twodaysoff:
        if j - i != 1: # if the day is NOT the previous day before the off-days
            starttime1 = np.random.randint(0, 23) + i * 24
            endtime = starttime1 + time_8h
            shift[i] = (starttime1, endtime)
            # else:
        if j - i == 1 and j != 6: # if the days is the day before the off-days
            starttime1 = np.random.randint(0, 16) + i * 24 #not start work withing 8 hours before midnight of off
            endtime = starttime1 + time_8h
            shift[i] = (starttime1, endtime)
            # add
            if starttime1 - shift[i - 1][1] < 12:  # 12 hours break btw work days
                # print('yes')
                # shift[i-1][0]=np.random.randint(0,starttime1-12) +i*24
                shift[i - 1][0] = np.random.randint(0, 10) + i * 24
                # print(shift[i-1][0])
                shift[i - 1][1] = shift[i - 1][0] + time_8h

                # print(shift[i])
        if j == 6:
            shift[j] = [0, 0]
        if j == 1:
            shift[j - 1][0] = (np.random.randint(0, 17))  # 0..16 24-8
            shift[j - 1][1] = shift[j - 1][0] + time_8h
    return shift

def modify_shift8h():
    mod_shift8h = shift8h()
    #print("old:", a)
    for i in range(1, len(mod_shift8h) - 1):
        if abs(mod_shift8h[i][0] - mod_shift8h[i - 1][1]) < 12 and np.array_equal(mod_shift8h[i],
                                                    np.array([0, 0])) == False:  # and mod_shift8h[i][0]-a[i-1][1]!=0:
            mod_shift8h[i - 1][1] = mod_shift8h[i][0] - 12 - np.random.randint(0, 4)
            mod_shift8h[i - 1][0] = mod_shift8h[i - 1][1] - time_8h
    return mod_shift8h

modify_shift8h()

It does not work on twodaysoff=[0,4] and twodaysoff=[0,3]