Updated timestamp.py for Sublime Text 3. Automatically add (if you have the correct code in your template) and update timestamps to mark the date a file was created and date it was last modified.

timestamp2.py

"""
Automatically add and update time stamps in your files.
On file open, will replace [timeStamp] with the current date and time.
Currently looks for two instances of this (example below).

To use, place the text [timeStamp] in your template file where you want it.
ex.
// CREATED: timeStamp
// MODIFIED: timeStamp

When you open this file for the first time, both [timeStamp] will change to
the current date and time. Every save, the MODIFIED line will update.

NOTE: After installing, don't open this file in Sublime Text because it will change
[timeStamp] in the code to the current time. Oops =]
"""
import datetime
import sublime
import sublime_plugin

TIMESTAMP_CODE = 'timeStamp'
TIMESTAMP_PATTERN = 'MODIFIED:\\s*20[0-9][0-9]-\\d+-\\d+\\s+\\d+:\\d+:\\d+(\\.\\d+)?'

class InsertTimestampListener (sublime_plugin.EventListener):
    """
    When opening file, search for TIMESTAMP_CODE and replace it with current time
    """
    def on_load (self, view):
        region = view.find (TIMESTAMP_CODE, 1)
        if region :
            replacement = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')
            with Edit(view) as edit:
                edit.replace (region, replacement)
        region = view.find (TIMESTAMP_CODE, 1)
        if region :
            replacement = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')
            with Edit(view) as edit:
                edit.replace (region, replacement)

class UpdateTimestampListener (sublime_plugin.EventListener):
    """
    On save, search for the MODIFIED line, and replace timestamp with current time
    """
    def on_pre_save (self, view):
        region = view.find (TIMESTAMP_PATTERN, 1)
        if region :
            timestamp = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')
            replacement = 'MODIFIED: %s' % timestamp
            with Edit(view) as edit:
                edit.replace (region, replacement)

# edit.py
# buffer editing for both ST2 and ST3 that "just works"
# cortesy of "Edit.py" ST2/3 Edit Abstraction. See: http://www.sublimetext.com/forum/viewtopic.php?f=6&t=12551

import sublime
import sublime_plugin
from collections import defaultdict

try:
    sublime.edit_storage
except AttributeError:
    sublime.edit_storage = {}

class EditStep:
    def __init__(self, cmd, *args):
        self.cmd = cmd
        self.args = args

    def run(self, view, edit):
        if self.cmd == 'callback':
            return self.args[0](view, edit)

        funcs = {
            'insert': view.insert,
            'erase': view.erase,
            'replace': view.replace,
        }
        func = funcs.get(self.cmd)
        if func:
            func(edit, *self.args)


class Edit:
    defer = defaultdict(dict)

    def __init__(self, view):
        self.view = view
        self.steps = []

    def step(self, cmd, *args):
        step = EditStep(cmd, *args)
        self.steps.append(step)

    def insert(self, point, string):
        self.step('insert', point, string)

    def erase(self, region):
        self.step('erase', region)

    def replace(self, region, string):
        self.step('replace', region, string)

    def callback(self, func):
        self.step('callback', func)

    def run(self, view, edit):
        for step in self.steps:
            step.run(view, edit)

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        view = self.view
        if sublime.version().startswith('2'):
            edit = view.begin_edit()
            self.run(edit)
            view.end_edit(edit)
        else:
            key = str(hash(tuple(self.steps)))
            sublime.edit_storage[key] = self.run
            view.run_command('apply_edit', {'key': key})


class apply_edit(sublime_plugin.TextCommand):
    def run(self, edit, key):
        sublime.edit_storage.pop(key)(self.view, edit)