Is it possible to create a timer trough a service or websocket?
I don’t believe there is a way to programmatically create an entity via the ws api.
But what it is you want to achieve? Creating (persistent) timers on external demand does not seem like a logical thing to do. If you do it 10 times a day you’ll be stuck with over 3500 timer entities after a year. And what is going to use the timers you created that way? If there are no automations using the timer helpers they are pointless.
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We are creating a plugin for the Athom Homey ( https://homey.app/ ) which has a flow system with the idea of node-red. and it would be nice to create a time on the "then"statement “then create a timer named x with xx minutes” or delete the helper "then delete timer named " but i don’t think its possible 
If you use Homey advanced flows instead of Home Assistant automations, it would be logical to do the timers in Homey too. Because that is where the flow is controlled. As I said before, a timer in HA alone is nothing, after that ends something needs to happen too. So you’d also need to create something to react to the timer, something to restart it if needed for the flow, and something to cancel or delete it as you said. All of that makes little sense if automating is done in Homey. That, and Home Assistant timers don’t come close to the Homey Chronograph app functionality 
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