It's a small amount of exercise BUT...
Exercise provides two things:
- it keeps an animal physiologically healthy. Strong heart and other muscles, lower weight etc.
- it keeps a dog mentally healthy because it is mentally tiring
It's quite possible to provide both on 2 x 30 mins walk a day provided the walk is rigerous with plenty of free running. That takes care of being physically healthy.
The walks also need to be stimulating, so no trudging round the same area over and over, preferably with play and/or training. It requires the humans to be actively engaged in the walk so no day dreaming or phone watching
. Plus the dog is likely to need other mental acitivies outside of the walk, such as training games or feeding games. In all honesty, once you do all that then 2 x 60 mins walking seem like the easier option 
Whilst all dogs are individual it's worth considering what the dog's breed has been selected for...
a) human companionship; lap dogs tend to 'need' less exercise than other breeds, even if they would enjoy a bit more than that.
b) periods of inactivity, punctuated by sudden activity, such as guardian breeds that typically spend their days static until a threat presents itself and then - bam! - sudden activity
c) several hours of continuous work but then expected to be quiet and no trouble (gun dogs, such as poodles fit here), so will require higher excerise and mental work before being calmer in the house
d) all day lower level of activity, often punctuation by short burst of higher level. Looking at terriers here who would typically be expected to look for their own work on a farm so should be expected to want to doing something for most of the day, with occasional opportunities to do something very high energy/excitement
e) looong periods of high octane activity. Utility breeds, such as huskies fit here.
A cavapoo might be more companion type that copes well on 2 x 30mins a day and plenty of fuss and cuddles; or more gun dog type that is going to look for its own entertainment if not provided with more by its owner, expect this type to do much better on something like 2 x 1hr good run outs plus training sessions.