How to find missing files between specific date range?

# presuming that the files are e. g. template-2017-07-01-16:

# To test a given date
for file in template-2017-07-01-{00..23}; do
  if ! [[ -f "$file" ]]; then
    echo "$file is missing"
  fi
done

# To test a given year
year=2017
for month in seq -w 1 12; do
    dim=$( cal $( date -d "$year-$month-01" "+%m %Y" | awk 'NF { days=$NF} END {print days}' )
    for day in $(seq -w 1 $dim); do
        for file in template-${year}-${month}-${day}-{00..23}; do
           if ! [[ -f "$file" ]]; then
             echo "$file is missing"
           fi
        done
    done
done

On a GNU system:

#! /bin/bash -
ret=0
start=${1?} end=${2?}
t1=$(date -d "$start" +%s) t2=$(date -d "$end" +%s)

for ((t = t1; t < t2; t += 60*60)); do
  printf -v file '%(%F-%H)T' "$t"
  if [ ! -e "$file" ]; then
    printf >&2 '"%s" not found\n' "$file"
    ret=1
  fi
done
exit "$ret"

Note that on the day of the switch to winter time (in timezones that implement daylight saving), you may get an error message twice if a file is missing for the hour of the switch. Fix $TZ to UTC0 if you want 24 hours per day for every day (for instance, if whatever creates those files uses UTC time instead of local time).

What about command like below:

 grep -Fvf <(find * -type f \( -name "2017-07-02-00" $(printf " -o -name %s" 2017-07-02-{01..23}) \)) \
           <(printf "%s\n" 2017-07-02-{00..23})

ls
2017-07-02-01  2017-07-02-06  2017-07-02-08  2017-07-02-14  2017-07-02-19
2017-07-02-04  2017-07-02-07  2017-07-02-11  2017-07-02-15  2017-07-02-22

The output after command ran:

2017-07-02-00
2017-07-02-02
2017-07-02-03
2017-07-02-05
2017-07-02-09
2017-07-02-10
2017-07-02-12
2017-07-02-13
2017-07-02-16
2017-07-02-17
2017-07-02-18
2017-07-02-20
2017-07-02-21
2017-07-02-23

Above we are generating all possibilities of 24 files using printf and pass it to find its -name parameter which printf also helping her, then with grep command we are printing those files are exist in our pattern but find didn't find them.