How to make Timer switches

1int Relay = 12;
2int btn1 = 4;
3int btn2 = 5;
4int btn3 = 6;
5int  btn4 = 7;
6int btn5 = 8;
7
8int relay1 = LOW;
9
10void setup(){
11pinMode(Relay,OUTPUT);
12pinMode(btn1,INPUT);
13pinMode(btn2,INPUT);
14pinMode(btn3,INPUT);
15pinMode(btn4,INPUT);
16pinMode(btn5,INPUT);
17}
18
19void  loop()
20{
21if(digitalRead(btn1) == HIGH)
22{
23digitalWrite(Relay,HIGH);
24delay(300000);                   // 5 min
25digitalWrite(Relay,LOW);
26}
27else if(digitalRead(btn2)  == HIGH)
28{
29digitalWrite(Relay,HIGH);
30delay(600000);                   //  10 min              
31digitalWrite(Relay,LOW);
32}
33else if(digitalRead(btn3)  == HIGH)
34{
35digitalWrite(Relay,HIGH);
36delay(1200000);                  //  20 min , 20x1000x60
37digitalWrite(Relay,LOW);
38}
39else if(digitalRead(btn4)  == HIGH)
40{
41digitalWrite(Relay,HIGH);
42delay(1800000);                 //  30 min
43digitalWrite(Relay,LOW);
44}
45else if(digitalRead(btn5) == HIGH)
46{
47relay1  = ~ relay1;             // ON/OFF
48digitalWrite(Relay,relay1);
49delay(500);
50}
51
52}
53