need help comparing values in different lines

Hello all,

I am a new (very new) user of awk and I am trying to write a if statement th
at will store a value in a variable, skip to the next line and store that sa
me value (but different line) and then compare the two.  If they are equal t
hen loop again, if they are not equal then print the line.  I will show you 
what the data looks like.  I am looking at the hour/minute field.  I want to
 be able to only print out the line when the first value on each minute chan
ges.  I want to skip the repeats of the minute.  Thanks for the help.

05 09 2006      0627  26 59.9890-111 25.715   396
05 09 2006      0627  26 59.9790-111 25.696   397
05 09 2006      0627  26 59.9690-111 25.677   398
05 09 2006      0627  26 59.9580-111 25.657   399
05 09 2006      0628  26 59.9480-111 25.638   400
05 09 2006      0628  26 59.9370-111 25.619   401
05 09 2006      0628  26 59.9260-111 25.599   402
05 09 2006      0628  26 59.9150-111 25.580   403
05 09 2006      0628  26 59.9050-111 25.561   404
05 09 2006      0629  26 59.8950-111 25.541   405
05 09 2006      0629  26 59.8860-111 25.521   406
05 09 2006      0629  26 59.8770-111 25.500   407
05 09 2006      0629  26 59.8670-111 25.478   408
05 09 2006      0630  26 59.8580-111 25.458   409
05 09 2006      0630  26 59.8480-111 25.438   410
05 09 2006      0630  26 59.8370-111 25.418   411
05 09 2006      0630  26 59.8270-111 25.399   412
05 09 2006      0630  26 59.8150-111 25.380   413
05 09 2006      0631  26 59.8040-111 25.362   414


The hour/minute is the fourth field over looks like (0631)