public extension Numeric {
    public var minsInSecs: Self {
        return self * 60
    }

    public var hoursInSecs: Self {
        return self.minsInSecs * 60
    }

    public var daysInSecs: Self {
        return self.hoursInSecs * 24
    }

    public var weeksInSecs: Self {
        return self.daysInSecs * 7
    }
}

import Foundation

public extension Int {
    public var minsInSecs: Int {
        return self * 60
    }

    public var hoursInSecs: Int {
        return self.minsInSecs * 60
    }

    public var daysInSecs: Int {
        return self.hoursInSecs * 24
    }

    public var weeksInSecs: Int {
        return self.daysInSecs * 7
    }
}

public extension TimeInterval {
    public var minsInSecs: TimeInterval {
        return self * 60
    }

    public var hoursInSecs: TimeInterval {
        return self.minsInSecs * 60
    }

    public var daysInSecs: TimeInterval {
        return self.hoursInSecs * 24
    }

    public var weeksInSecs: TimeInterval {
        return self.daysInSecs * 7
    }
}

--- 
+++ 
@@ -1,37 +1,17 @@
-import Foundation
-
-public extension Int {
-    public var minsInSecs: Int {
+public extension Numeric {
+    public var minsInSecs: Self {
         return self * 60
     }
 
-    public var hoursInSecs: Int {
+    public var hoursInSecs: Self {
         return self.minsInSecs * 60
     }
 
-    public var daysInSecs: Int {
+    public var daysInSecs: Self {
         return self.hoursInSecs * 24
     }
 
-    public var weeksInSecs: Int {
+    public var weeksInSecs: Self {
         return self.daysInSecs * 7
     }
 }
-
-public extension TimeInterval {
-    public var minsInSecs: TimeInterval {
-        return self * 60
-    }
-
-    public var hoursInSecs: TimeInterval {
-        return self.minsInSecs * 60
-    }
-
-    public var daysInSecs: TimeInterval {
-        return self.hoursInSecs * 24
-    }
-
-    public var weeksInSecs: TimeInterval {
-        return self.daysInSecs * 7
-    }
-}
Use Numeric over Int and TimeInterval
