DateComponent.vue

<template>
    <div id="date-component">
        <form>
            <label>Start</label>
            <input
                type="datetime-local"
                name="start_date"
                v-model="start_date"
            />
            <label>End</label>
            <input
                type="datetime-local"
                name="end_date"
                v-model="end_date"
            />

            <p>Diferencia en días: {{ differenceDate }}</p>
        </form>
    </div>
</template>

<script>
    import {mapGetters} from 'vuex';
    export default {
        name: 'date-component',
        computed: {
            ...mapGetters(['differenceDate']),
            start_date: {
                get () {
                    return this.$store.state.DateModule.start_date;
                },
                set (value) {
                    this.$store.commit('SET_START_DATE', value);
                }
            },
            end_date: {
                get () {
                    return this.$store.state.DateModule.end_date;
                },
                set (value) {
                    this.$store.commit('SET_END_DATE', value);
                }
            }
        }
    }
</script>

<style scoped>
    #date-component * {
        font-size: 25px;
    }
</style>