My LR Pro Timer 3 arrived today, but when I turned it on for the first time, I saw that the battery was at minimum capacity. So, using a USB-A / USB-C cable, I plugged it into a 20.0W Max (Output: 5V⎓3A 9V⎓2.22A 12V⎓1.67A) port on a charging block.
1) How long will it take to charge?
2) Can, or should it, be charged using the higher voltage PD USB-C (100.0W Max (5V⎓3A 9V⎓3A 12V⎓3A 15V⎓3A 20V⎓5A) port and a PD cable?

No, you can't charge it via PD or USB-C to USB-C cable.
Please use a USB-A to USB C cable only. You can monitor the charging progress, when you turn the device on. You can get detailed information when going to the Status screen.