Format decimal day as 24-hour HH:MM:SS
mysql&gt; SELECT SEC_TO_TIME(86400 * .51923075705577);
+--------------------------------------+
| SEC_TO_TIME(86400 * .51923075705577) |
+--------------------------------------+
| 12:27:41.537410                      |
+--------------------------------------+

(There are 86400 seconds in a day.)
mysql&gt; SELECT SEC_TO_TIME(86400 * 0.999999);
+-------------------------------+
| SEC_TO_TIME(86400 * 0.999999) |
+-------------------------------+
| 23:59:59.913600               |
+-------------------------------+

mysql&gt; SELECT SEC_TO_TIME(86400 * 0.001);
+----------------------------+
| SEC_TO_TIME(86400 * 0.001) |
+----------------------------+
| 00:01:26.400               |
+----------------------------+

To avoid fractional seconds:
+---------------------------------------------+
| SEC_TO_TIME(ROUND(86400 * .51923075705577)) |
+---------------------------------------------+
| 12:27:42                                    |
+---------------------------------------------+
+---------------------------------------------+
| SEC_TO_TIME(FLOOR(86400 * .51923075705577)) |
+---------------------------------------------+
| 12:27:41                                    |
+---------------------------------------------+