In Swift you can easily separate a String into an array by slicing it at a certain character:
let startDate = "23:51"
let startDateAsArray = startDate.components(separatedBy: ":") // ["23", "51"]`
let startDate = "23:51"
let startArray = startDate.componentsSeparatedByString(":") // ["23", "51"]`
Or when the separator isn't present:
let myText = "MyText"
let myTextArray = myText.components(separatedBy: " ") // myTextArray is ["MyText"]
let myText = "MyText"
let myTextArray = myText.componentsSeparatedByString(" ") // myTextArray is ["MyText"]