VueJS Countdown timer setInterval resets date input field?

hi guys. question. hope that anyone would be able to help.

I've got a component in which i've made a countdown timer. On the data property i have defined now: null, then on the mounted hook i'm calling

        setInterval(() => {
                this.now =  Math.floor((new Date()).getTime() / 1000);
            }, 1000);

All fine and the timer works with some extra logic. however when I try to fill an input of type date with v-model to another property in the data object it resets every seconds. other input fields do not? any suggestions??