time.delta() not compatible with .run_if() and timer conditions

[ngreve]

Bevy version

0.10.1

What you did

use bevy::{
    prelude::*,
    utils::Duration,
    time::{common_conditions::*},
};
use text_colorizer::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_system(system_foo.run_if(on_timer(Duration::from_secs_f32(2.5))))
        .run();    
}

fn system_foo(time: Res<Time>) {
    println!("{}: Seconds since last update: {}","foo".blue() , time.delta().as_secs_f64());
    println!("FPS: {}", 1.0 / time.delta().as_secs_f64());
}

What went wrong

Maybe this is expected behavior, but in the given example
time.delta() shows the wrong delta, but visually the console output appears correctly every ~2.5 seconds.
I would expect time.delta() to be close to the configured 2.5 seconds, too.

In my case the console outputs:

foo: Seconds since last update: 0.00117275
FPS: 852.6966531656363
foo: Seconds since last update: 0.001393651
FPS: 717.5397570840906

[rlidwka]

There's no way currently to get time delta between two executions of the same system.

• for systems that execute every tick there's Time
• for systems that execute on a fixed schedule there's FixedTime
• for systems running on condition there's nothing
• for systems that execute in a custom schedule there's also nothing (I'm making my own Time equivalent for each schedule I create for this purpose)

I don't mind having single solution for all four use-cases, but I don't know bevy codebase enough to suggest it.

[MWFIAE]

Can be solved by adding a 'Local` to the system that keeps track of the last time the system was called. I don't think its common enough to warrant any changes in the framework, and additionally its simple enough of a pattern to just use it when it is actually needed.