Dynamically assigning the timer interval - vb.net

Question

I have a function that needs to be run for every 15 minutes using the timer in VB.net.
But the challenge present here is, if i start the timer, say at 2:00 AM, the actual function will be executed at 2:15 AM after which the same function will be executed for every 15 mins.
I have a sub "Timer" in which the timer is started and the Addhandler operator calls the "ONhandler" function for every 15mins.
private mytimer as timer
private sub Timer()
{
with mytimer
.autoreset=true
.enabled=true
.interval=900000
.start
end with
AddHandler mytimer.elapsed ,assressof onhandler
console.readkey()
}
onhandler(byval source as oblject,byval e as elapsedeventargs)
{
Performs the DB operations.
}
Initially I had a couple of logic that would start the timer exactly at every 00,15,30,45th mins of each and every hour. Assuming that I start the application at 1:55AM, the logic would ensure that the applications sleeps till it reaches 2:00AM and at 2:00 AM, the timer would start. After 15 mins, i.e 2:15AM, the function will get executed.
But what I need is , I dont want my application to wait for 15 mins from 2:00 till 2:15. Instead it should process at 2:00 and then start the timer. To overcome this, I had included a new function "onhandler" with same name of AddHandler method which does the same process.
private sub Timer()
{
onhandler() ****New function namesd as AddHandler method
with mytimer
.autoreset=true
.enabled=true
.interval=900000
.start
end with
AddHandler mytimer.elapsed ,assressof onhandler
console.readkey()
}
onHandler()
{
Do same DB function
}
After implementing the new logic,
if I start the application at 1:55 AM, my app would sleep till 2:00 AM after which the Onhandler() method inside sub will get executed first and it would get completed at 2:01Am.
Now the timer is started for 15 mins and the the next set of process is executed at 2:16AM as the timer is set for a 15 min interval. But I need my process to run exactly at 2:15AM. In other words, the timer interval must be for 14mins and not 15 mins.
another example is, I start the application at 3AM and if it ends at 3:03Am, then the time must have an interval of 12 mins and not 15 mins, for the next run.
IS there any way to make the timer interval dynamic for each and every time the process gets completed based on the process ending time???
PS : I am new to DotNet and have been cracking my head on this issue for the past few days. Guys, kindly help me out here.
Thanks in advance,
Madhu.

Answer 1

The correct way to do this would be to run a Windows Task at specific times. But if you really want to write this in your application, you could wake your program every minute to check the time and just add this to the called method:
Dim d = DateTime.Now
if(Not (d.Minute = 0 OrElse d.Minute = 15 OrElse d.Minute = 30 OrElse d.Minute = 45)) Then
Return 'Quits if the current time is not right
End If

Answer 2

I had something similar once. I would have a variable called NextExecutionTime which would contain the next time the process need to be executed.
At first it would be (example) 2am.
I would then have a timer every minute and if the current time was equal or greather than NextExecutionTime, I would execute the process and setup the NextExecutionTime variable to the next time I wanted the process to run.