A script for setting creation and modification dates on all files within a folder. Specify the first date in the script then all files are stamped in alphabetical order, increasing by 1s.

timestamp.sh

USAGE="Set the desired date/time in the script and then call: timestamp /path/to/folder"
DATE="022109002017" # month day hour min year

if (( $# != 1 )); then
    echo "Illegal parameters"
    echo $USAGE
    exit 2
fi

if [ ! -d $1 ]; then
  	echo "$1 is not a directory"
  	echo $USAGE
  	exit 2
fi

SEC=0
# run through all files in the directory in ls order i.e. alphabetically
for i in $( ls "$1" ); do
	TIMESTAMP=$(date -v"$SEC"S -j $DATE '+%m/%d/%y %H:%M:%S')
	FILE="$1/$i"
  # set both creation and modification timestamps
	SetFile -d "${TIMESTAMP}" -m "${TIMESTAMP}" "${FILE}"
  # increment the timestamp by 1 second
  SEC=$((SEC + 1))
done

exit 0

Hmm... I start getting errors after 60 images:

60S: Cannot apply date adjustment
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
            [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
ERROR: invalid date/time
61S: Cannot apply date adjustment
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
            [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
ERROR: invalid date/time
62S: Cannot apply date adjustment
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
            [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
ERROR: invalid date/time

This seems to work for me:

TOTAL_SECONDS=0
# run through all files in the directory in ls order i.e. alphabetically        
for i in $( ls "$1" ); do
  MIN=$((TOTAL_SECONDS / 60))
  SEC=$((TOTAL_SECONDS % 60))
  TIMESTAMP=$(date -v"$MIN"M -v"$SEC"S -j $DATE '+%m/%d/%y %H:%M:%S')
  FILE="$1/$i"
  # set both creation and modification timestamps                               
  SetFile -d "${TIMESTAMP}" -m "${TIMESTAMP}" "${FILE}"
  # increment the timestamp by 1 second                                         
  TOTAL_SECONDS=$((TOTAL_SECONDS + 1))
done

I modified this a bit to increment hours as well,

# Run through all files in the directory in ls order i.e. alphabetically.        
for i in $( ls "$1" ); do
  HOUR=$((TOTAL_SECONDS / 3600))
  MIN=$(( ((TOTAL_SECONDS / 60)) % 60 ))
  SEC=$((TOTAL_SECONDS % 60))

  FILE="$1/$i"
  
  # Set both creation and modification timestamps.
  TIMESTAMP=$(date -v"$HOUR"H -v"$MIN"M -v"$SEC"S -j $DATE '+%m/%d/%y %H:%M:%S') 
  SetFile -d "${TIMESTAMP}" -m "${TIMESTAMP}" "${FILE}"

  # Leaving a gap of few minutes makes it possible to insert additional media 
  # to Google Photos later. This has to be in the magnitude of minutes because 
  # Google Photos doesn't allow changing the seconds value when updating a 
  # media's timestamps.
  TOTAL_SECONDS=$((TOTAL_SECONDS + 300))
done

By the way, is anyone else still using this script? For some reason, Google Photos orders videos by their Last Opened timestamp, completely ignoring their created and modified timestamps. I had to spend many hours manually editing the timestamp of each video in my album.

I wish SpeakerDeck supported videos.