It is 1.7 Km between these stations so you could risk metro but 20 mins is very tight. Taxis take about 7 mins (traffic permitting) for about 10 euro.

Just check seat61.com for full details.

https://www.seat61.com/stations/milan-porta-garibaldi.htm

But I have also checked Metro will go from Milano P Garibaldi and it will take 5 mins to reach Milano Centralle. 
 

Further, any customer care number to speak with Eurail executive to take further help on my query. If possible guys pl share…

There is no phone support.

The link posted above gives you all the information required and that site is run by someone whose information is normally very accurate.

Walking is out, it’s too far and there sounds like little to choose between metro and taxi but I am not familiar with the station layouts or Milan traffic so...

As @Yorkie said, a 20 minute connection from one station to another like that is exceptionally short, even for someone familiar with both stations. Is it possible, maybe, if it were me, I’d have a plan for the likely scenario that it is not possible.

It will take much more time to buy the metro ticket as the trip itself.

BUT-as I am now also in IT, close by-there is-again, its getting tiresome but the local habit- a STRIKE = Scioperta announced for today-not so much for TrenItalia, but the local transit etc-at varying times. Check TreNord and ATM-MIlano=the metro/tram operator.

Also that treno dalle VNz will make more stops in Milano-and will be late (I stay in Brescia, where they all pass by)-15 to 20 mins seems to be the norm. Check if it also stops LAMbrate=shortens the time on it and has many -if they run-treni locale diretto per Centrale.

But all is not lost-ask to change the ticket for the EC-they run ev 1 or 2 hrs, and if not-take regional till CHIASSO=border point, from there reliable and RES free (even on same treni) in the Swiss. It also seems there is some special rule for these cases-as result of the scioperta!

Your connection is very risky - in Milano you can get a delay on the last km as the stations are busy and there are frequently delays in the end… so if your train is 5 mins delayed, you can already skip the plan to catch your train.
If it is on time and you are not a slow walker, then it is no problem to walk that 1,7km and catch the train in Centrale. Way is very easy, just probably you have to cross 1-2 times a red light to make it. 
Anyway - if not, as others said, there are many extra options to get to Zürich from Milano (without a reservation as well).

I see the rail planner app really gives this connection. It even claims it's a transfer by public transport that takes just 15 minutes. However 15 minutes is only possible if you don't have to buy a metro ticket, you know your way in both stations and if there's a metro right when you arrive at the metro platform. In other words, much too short.

Trenitalia doesn't give this connection. Neither do DB and ÖBB; DB and ÖBB say it's a 35 minute transfer between the 2 stations, which is much more realistic IMO.

@Nanja, where does the app get its minimum connection times from? It looks like in this example, the MERITS data would say 35 minutes, since DB and ÖBB use that, so I'd expect the rail planner app to use the same value.

For Support, in this case you can ask for help at the train station the staff of Trenitalia, the train company that runs the trains in Italy. 

The next time, if possible, take the direct Eurocity train from Zürich to Venice that starts at 6:33 in Zürich. 

Hi rvdborgt, I will look into it and get back to you on this. 

@Mukhammad @Camilo. 

The rail planner app still claims you only need 15 minutes in Milan to get from Centrale to Garibaldi. This needs to be corrected because that is clearly not correct. See my post above for more info.

Hi @rvdborgt,

Apparently the transfer time from Milano Centrale to Milano Porta Garibaldi shows the same (15 mins) on both DB's and ÖBB's websites.

@Mukhammad 

That's strange - that means it was changed since I looked it up several months ago. However, the distance is still 1.7 km, which cannot realistically be covered on foot in 15 minutes.

In addition, Trenitalia don't offer such short changes between Porta Garibaldi and Centrale themselves, so there's still something wrong. Possibly Trenitalia are now including the incorrect minimum connection time in the MERITS data. Could you please check with Trenitalia?

@rvdborgt 

I already checked the Trenitalia that they don't have the same connections as shown on Eurail Planner/ÖBB/DB. In this case, the matter about the transfer time in between those stations has been raised to my superior.

Have a nice day!