According to Epilator Central http://www.epilatorcentral.com/epilator-tips-how-to-use-an-epilator/, it takes about 30 minutes to do both of your legs, but the very first time it can take a little bit longer as are not yet experienced.
It’s very important to choose a very good quality epilator. Pick a well-known, well-reviewed brand that you know you can trust. A cheap epilator may not work as well and it may be more painful to use and also could be slower to epilate. Since your epilator will last a long time (and you won’t have to buy wax and fancy razors) it’s worth springing for a good one.https://www.wikihow.com/Epilate-Legs
How often you epilate depends on one’s hair growth and is a personal preference. Beginners would do well to epilate once a fortnight. Doing it frequently has two benefits: your pain threshold increases (as shorter hair causes less pain plus your skin gets used to the ‘tugging’) and your overall hair growth reduces over time. Later you might need to do it only once a month. https://gulfnews.com/lifestyle/fashion/10-top-epilation-tips-1.790029