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As for your question, assuming that your data is in Row 2, this should work:
=IF((C2-A2)*24+D2-B2<48,"Less than 48 hours","More than 48 hours")
It first determines the difference between your Date cells in hours via (C2-A2)*24, then adds to that the difference between your times via D2-B2 to get the total elapsed time in hours. If D2-B2 is negative, it will be subtracted from (C2-A2)*24.
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