I used to follow this advice to the letter. That
was back when I had recently established
raised rose beds. Newly planted (the previous
fall or that spring), mostly bareroot roses did great
over winter and in cooler temps, started dropping
like flies in the high heat/sun. Eventually I lost
10 or 12 out of 16 roses planted in my first ever
rose bed.

Finally I checked with a local rosarian (we
happened to be in the same ladies' golf group
then) who looked at me like I was crazy and
said in that kind of heat she watered every other
day! And she breeds her own roses, so not
exactly an amateur.

Long story short: Whatever it says in the books
might well work in most conditions, but not at
the extremes (especially of heat) AND with
raised beds AND using a fairly lightweight soil.
(I also learned to add back in some clay.)

So if you live in a hot area and you can water
extra, do so.

Gail
near San Antonio TX Zone 8