TimeIntervalFromSRT.swift

import Foundation

func extractTimeInterval(from string: String) -> TimeInterval? {
    let formatter = DateFormatter()
    formatter.dateFormat = "HH:mm:ss,SSS"
    guard let date = formatter.date(from: string) else { return nil }
    guard let referenceDate = formatter.date(from: "00:00:00,000") else { return nil }

    let interval = date.timeIntervalSince(referenceDate)
    return interval
}

let timingStr = "00:00:53,266 --> 00:00:56,266"
let components = timingStr.components(separatedBy: " --> ")
let intervals = components.map({ return extractTimeInterval(from: $0) })
print("intervals: \(intervals)")

// prints: intervals: [Optional(53.26600003242493), Optional(56.26600003242493)]