Another Tri Noob

Welcome Mark, well to find your times, you'll need to do some time trials. 

Next time you swim, swim an 800 all out. Once you finish record the time. take the time, and divide by 10. this will give you a number, now take the result will be Time in Minutes per 100 yards.  Multiple by that 5 and get the result in Yards, Once you get that just multiple the yards by 1.1 (Rounded even though (1m = 1.09 yards)) to give you Meters. That will give you the time to swim that leg. (lets say 10 mins) 

Next, you'll have to do a time trial on how fast you can ride your 20k (12.4 Miles). lets say you ride that at 18MPH, that will take you 12.4 Miles / 18 MPH = .6888888  Now multiply that by 60 mins to give you minutes = 41'19".

Now lets say it takes you 28 mins to run a 5k, now the formula for that is Distance/Time in hours. So take the distance in Miles 3.1/(28Mins/60Mins)= 6.6  = Mph  or a pace of 9:03 Mins / Mile 

Finally, just the time it's going to take you to change out from your swim gear, and into the B ike gear, and the same from change out of your bike gear to run gear. Give yourself ~ 3 mins  for a total of 

So, if you're within these i'd say at least 1 hour 23 mins give or take. 

Good luck!

Scott