Yes, you can buy up to three Elixirs at once from Gaile at the Foothill stable, which is conveniently at the base of Death Mountain. She'll also explain the checkpoint system, so you'll know when to use them. When you buy from Gaile, the elixirs are 60 rupees for one, 110 for two, and 150 for three. Each elixir lasts for 6 minutes and 10 seconds.