To get the shortest JBL Go 3 charge time, use at least a medium current USB charger.
JBL Go 3 Charge Time: How Long to Fully Recharge
According to the specs, the time it takes to charge this speaker is two hours and thirty minutes (2.5 hours). This is using a 5 watt charger (5 volts, 1 amp). Charging times get longer if your adapter does not provide lower power than this. E.g. You could more than double the charge time if your charger only delivers a maximum current of 500 milliamps.

How Long the JBL Go 3 Plays Per Full Charge
On a complete charge, this speaker can play for up to five (5) hours. This is thanks to its 2.775 watt-hour lithium ion polymer battery. But when you play it loudly, especially with extra bass, you will get shorter play time per charge.
We’ve seen this Bluetooth speaker run dead in around 8 hours when played at louder volumes, especially with bassy music. So to get the longest charge time, power saving is key. Just play it only as loudly as you must, to hear it well throughout your listening space.

The JBL Go 3 Charge Time Gets Smaller As it Ages
If you own this speaker over a few years, you may notice that the play time per charge is shorter. This is normal for devices like this one, that rely on lithium ion batteries.
But by exercising the battery, you can slow this charge drop off.
To exercise the JBL Go 3, run the battery dead first. Then recharge it. Do this again every three to six months when not in use.
Also, we suggest that you NOT leave the speaker plugged into a charger once it hits full charge. Thus, right after the charging lamps completely go out, disconnect the speaker as soon as you can. Why? Because this avoids overcharging it and possibly damaging the battery.