There is not a straightforward answer to this question. As we are sure you already know, all electronics that are in bypass mode take a bit of time to power up when you turn them on. To avoid this issue, manufacturers have designed their tuners in such a way so that they are always kept powered up.
This way, when you decide to tune your guitar, you can do so in a matter of seconds, without having to wait for the device to "wake up". One aspect that you should be aware of is the fact that when in bypass, these pedals do not consume that much energy so that the battery that powers them is completely drained.
In fact, most of these products have a battery life that ranges from 5 to 60 hours, depending on the type of battery that is used to power the tuner. You can ask the manufacturer of the model that you like for more info on this topic.