Google App Script Spreadsheets

Every part of the example below can be done more succinctly, efficiently, elegantly, and adaptably -- it's really not good code -- but I wanted to make the components as clear as possible so you can see how it works.

First, here's an oversimplified function to convert hours to 24 hour format. I don't recommend that you use exactly this because it'll only work with on-the-hour times formatted exactly as you wrote them, e.g. "3PM" or "2AM" -- "2:30 pm" would not work at all. For more sophisticated time conversion, check out this answer: convert 12-hour hh:mm AM/PM to 24-hour hh:mm

function oversimplified_time_format_converter(input){
  if(input.indexOf("PM")!==-1){
    var hour = 12 + (input.substring(0,input.indexOf("PM"))*1)
    if(hour>24){hour-=24}
  } else {
    var hour = input.substring(0,input.indexOf("AM"))
    }
  return hour
  }

Next, here's a function to perform the task you mentioned, which uses the oversimplified time format converter function above.

function yourFunction() {

  //First, locate your data:
  var sheet = SpreadsheetApp.openByUrl("https://docs.google.com/spreadsheet/yourspreadsheetURL").getSheetByName("YourSheetName")
  var cell = sheet.getRange("A1")
  var cell_contents = cell.getValue() //The cell contents will be "1PM -5PM"

  //Next, locate the cells where the results will go
  var first_cell_to_the_right = cell.offset(0,1) //This is cell B1
  var second_cell_to_the_right = cell.offset(0,2) //This is cell C1

  //Next, get the text, split it into separate strings
  var first_part = cell_contents.substring(0,cell_contents.indexOf(" - ")) //This will be "1PM"
  var second_part = cell_contents.substring(cell_contents.indexOf(" - ")+3) //This will be "5PM"

  //Now convert to 24-hour time format:
  first_part = oversimplified_time_format_converter(first_part)
  second_part = oversimplified_time_format_converter(second_part)

  //Now write the results to your spreadsheet
  first_cell_to_the_right.setValue(first_part) //Set value of B1 to "1PM"
  second_cell_to_the_right.setValue(second_part) //Set value of C1 to "5PM"
}