Curl: (60) SSL certificate problem: certificate is not yet valid

Hey guys - I am trying to install to a new PI and getting the following error:

curl: (60) SSL certificate problem: certificate is not yet valid

curl performs SSL certificate verification by default, using a "bundle"
of Certificate Authority (CA) public keys (CA certs). If the default
bundle file isn't adequate, you can specify an alternate file
using the --cacert option.
If this HTTPS server uses a certificate signed by a CA represented in
the bundle, the certificate verification probably failed due to a
problem with the certificate (it might be expired, or the name might
not match the domain name in the URL).
If you'd like to turn off curl's verification of the certificate, use
the -k (or --insecure) option.

Obviously I don't want to turn off the verification - any thoughts or suggestions ? (could this be a DST time issue by chance?)

Also get the following error:

wget -O basic-install.sh https://install.pi-hole.net
--2016-09-10 02:38:36-- https://install.pi-hole.net/
Resolving install.pi-hole.net (install.pi-hole.net)... 104.24.109.83, 104.24.108.83, 2400:cb00:2048:1::6818:6c53, ...
Connecting to install.pi-hole.net (install.pi-hole.net)|104.24.109.83|:443... connected.
GnuTLS: A TLS fatal alert has been received.
Unable to establish SSL connection.

2016-09-10 02:38:36

You need to set the date on the Pi first, it's off by a half-dozen months or so. It should have automatically set itself via ntp, but the difference may be too big for ntp to accept as valid.

You nailed it - clock/date was way off !

Cheers !

FYI, somehow 2 of my Pi's were not syncing NTP anymore either and time was off:

$ grep ^server /etc/ntp.conf
server 0.debian.pool.ntp.org iburst
server 1.debian.pool.ntp.org iburst
server 2.debian.pool.ntp.org iburst
server 3.debian.pool.ntp.org iburst

One running Raspbian light for Pi-Hole and the other XBian (Jessie).
Had to restart ntpd on both Pi's to have it start syncing again.

My non armhf Debian Stretch laptop did not have any issues syncing.
But Stretch seems to grab NTP server list from "/etc/default/ntpdate" instead of non existing file "/etc/ntp.conf":

$ grep -v '#' /etc/default/ntpdate
NTPDATE_USE_NTP_CONF=yes
NTPSERVERS="0.debian.pool.ntp.org 1.debian.pool.ntp.org 2.debian.pool.ntp.org 3.debian.pool.ntp.org"
NTPOPTIONS=""