How can I lock a file / store a password for a period of time?
1 Create a good password:
Create a good and strong password
Long password with complex characters a-z A-Z 0-9 !@#$... more than 20 is good
You can also use this online tool to generate them online password generator
2 Encrypt your file:
You can encrypt your file using Windows encryption or even a WinRAR or other things)
3 Save the key for the future:
You can use sites like futureme.org or others to email your key(password) to you or anyone else you like to have access the key
I suggest to use multiple sites and times to ensure that you won't lose access to your file
A. You could set up an remote email account and throw away the key.
Put a crazy password on gmail (or any email service that you expect to still be in business when the time comes). Get it to send you a cryptographic key or to send you the password at a time that is programmed in the future.
Then you throw away the gmail password. No 2 factor authentication, no way of getting back in. The problem is that you have to rely on gmail.
Future mail: gmail calendar, lettermelater... http://www.tothepc.com/archives/ways-to-send-future-email-gmail-outlook-tools/
If it's under your control, you can "hack" the time.
The problem with a windows or local solution is that you can change the time or fake an ntp server. Anything that reboots either has to be told the time or can be updated with new time info.
So somebody else would have to run the clock. Having and external service to send you a message at a certain time is the answer I believe. The important thing is being sure that that external service is reliable and redundant when the time comes so that you don't lose the info forever.
Redundant could mean having two or more files with the data, with two different passwords, on 2 different hard drives, with two different remote email services from 2 different companies.... Basically doing your setup twice in 2 completely independent ways with no single point of failure.
Encryption has to do with security, not time.
Your question refers to a password. You can use a cryptographic key simply to increase the complexity and make so that it is not accessible via simple brute-force. That's beyond the subject and a bit complicated but it might interest you. pitt.edu/~poole/PGP.htmago
You could encrypt your data with PGP encryption and send yourself the encryption key later. If security is a concern, using an encryption key rather than a long password would be preferable.
If you are using a password, then having 10 characters or more that are random and include symbols and caps would be a minimum, in my estimation. The more random characters in your password (the longer it is), the better as it makes it exponentially more difficult to brute-force.
Beyond that, the stackexchange page referenced by Sam3000 is worth mentioning.
The free FileLocker might be a solution :
The FileLocker is a Windows NT/2000/XP/2003/Vista/7 32Bit command line tool to lock a file. The lock is a read/write/delete lock. The lock will be released once you kill the program or after a specified time / keypress.
FileLocker will lock the file for the duration of its execution. The locking will end when the program terminates, either when the specified time is up, or if the program is killed.
FileLocker [/T LockTime] [/I] [/K] [/Q] file [file...]
/T LockTime Time in milliseconds to lock the file
/I Infinite locking until process is killed (default)
/K Lock file until key is pressed
/Q Be quiet.
Both the binary and the source of FileLocker are available on the website.