Question
A pirate ship sets sail from island $A$ to island $B$. At the same time, another pirate ship starts sailing from island $B$ to island $A$. Assume each ship stays along the same path between the two islands. The pirate ships pass other at $1:00$ PM and continue on their paths. One of them arrives at $5:00$ PM, the other at $10:00$ PM. At what time did the pirate ships set sail? Put your answer in military time, excluding the $0$ if the hour is only one digit. For example, if the answer is $4:30$ PM, answer $1630$.