Most models these days will climb to thermal country in about a minute or less. To ensure you have some battery to run the on board gear it's likely wise to limit yourself to 4 climbs up of around a minute each. That will ensure you have power to run the radio and servos and enough to fight back to your location from downwind if you find yourself not watching where you're flying or miss the thermal you were trying to snag.
From there learn to fly smoothly and with minimal inputs so you don't drag the model down. And then learn to find and ride thermals.
The point of flying a glider is to learn to soar after all. Once you get to that point you'll likely find that you only ever need to use one or at most two climbs per pack anyway. After that it's stealing altitude from thermals and flying until your neck is sore which pushes you into landing.