PHP: How to print out "00:00:00" on start and 23:59:59 in the end?

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there is discrepancy on time that we are getting on it. we need to get starting time that is "00:00:00" and ending time that is "23:59:59".

for this problem the total stop time is 15:48:56 but were getting only is 07:15:26. (00:00:00 to 05:06:18) and (20:32:47 to 23:59:59), this is the missing data from the table grid. Heres the sample output that we need to get.

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thanks for the reply guys. hope you can help me TIA.