Not Excel, Helen but something that might be trivial enough for me to have a stab at although my head spins round looking at the numbers and I’m easily confused. I might have got this python attempt wrong, especially with your estimates, and I’m sure it could be done far better. I’ve included 8 as it reads the same both ways but I don’t think there is an instance where it can be reversed:

swaps = ['0', '1', '5', 'x', 'x', '2', 'x', 'x', '8', 'x']
  x = 0
  for hr in range(0, 24):
      for min in range(0, 60): 
          orig = str(hr).zfill(2) + str(min).zfill(2)
          rev = ""
          for i in reversed(range(0, 4)):
              num = int (orig[i])
              if swaps[num] == 'x':
                  rev = ""
                  break
              else:
                  rev = rev + swaps[num]
          if len(rev) == 4:
              revhr = rev[0:2]
              revmin = rev[2:4]
              if int (revhr) < 24 and int (revmin) < 60:
                  print (orig[0:2] + ":" + orig[2:4] + " - " + revhr + ":" + revmin)
                  x = x + 1
  print(x)

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