FlagService.swift

import UIKit

// MARK: Cache Service
struct FlagService {

    let key: String
    let bufferTime: Double

    var canProcess: Bool {
        let buffer: Double = bufferTime * 60 * 60
        guard (Date().timeIntervalSince1970 - getFlag()) > buffer else {
            logger.info("Not the time to Fetch for key: \(key)")
            return false
        }
        return true
    }

    init(key: String, bufferTime: Int = 12) {
        self.key = key
        self.bufferTime = Double(bufferTime)
    }

    func setFlag(_ value: Double = Date().timeIntervalSince1970) {
        Preference.set(value, forKey: key)
    }

    private func getFlag() -> Double {
        return Preference.double(forKey: key)
    }
}

Usage.

let flagService = FlagService(key: "pass your key here", bufferTime: 12) // 12 hours
flagService.setFlag() // this will set current time as flag 
flagService.getFlag() 
flagService.canProcess // this will tell to fetch or not.