Day trips during Golden Week

I have recently booked a holiday in Japan and have found out that part of it is during the Golden Week. Will it be possible to organise day trips from Kyoto to Hiroshima and/or Nagoya using Shinkansen during that period? And if so, on which days to travel and how much in advance should I book the seats?

Will it be possible to organise day trips from Kyoto to Hiroshima and/or Nagoya using Shinkansen during that period?

Yes, but on some days the trains are very busy.

And if so, on which days to travel and how much in advance should I book the seats?

Trains from Kyoto to Nagoya and from Hiroshima to Kyoto can be expected to be particularly busy on May 5 and 6. And in the opposite direction on May 3. On other days during the Golden Week it can also be very busy, but seats should be available if you make reservations several days in advance.

In case you cannot make seat reservations, you can always use non-reserved cars.