How long should it take to fully charge Samsung Galaxy Note 10.1?

It depends on how and where you charge it. It also depends on how depleted the battery is and what applications are running in the background.

For example, charging it at a house on the mains power on an empty battery can take about 1, 2 or 3 hours to charge, depending on whatever you have running in the background.

Charging from a laptop, computer or console is significantly slower, because they have a lower power output than mains power does. Because of this, a fully depleted battery can take about 4-6 hours to charge on a computer or console.

To make your device charge quicker, turn off WiFi, GPS and Bluetooth, as these use up a lot of background battery.

You may also want to edit your Data usage settings to restrict all your apps from consuming battery life in the background. it should be relatively easy to figure out how to do this.

Or, an easier way is to simply put your device into "Airplane Mode" while it is charging. this temporarily turns off all the background things that consume your battery (such as wifi, bluetooth, etc). Don't forget to turn off airplane mode after charging.

You may also want to consider lowering your screen brightness. believe it or not, the backlights in Samsung products are so powerful that they consume the most battery than anything else on the device.

Look into the "Power Saving" setting on the device too.