This is a cell modem only configuration, no wifi. I am using HiveMQ as the broker. If I use a wifi connection (temporaily) all works correctly. If I take out the wifi, then there is an error on the esp_mqtt_client_init. The broker host name is a long unique name like 84053a451db5xxxxxxbaa.s1.eu.hive...

axellin - This is an area I never have been in. Would you mind showing a line or two of code I would put in my Arduino sketch to effect this change. I would really appreciate your help.

A. I find it hard to believe it drifts over 20 minutes in 12 hours.
B. How do I make it work to be at least within a few minutes max?
C. How do I find out what the crystal is?

Here is the code I used. I want to wake in 12 hours. The actual time it woke up was 11:43. The value used for sleep time was 43200000000 but the acutal amount was 42180000000 (if I did all the math correctly). How do I get the 12 hours required? uint64_t toSleep = 43200000000; esp_sleep_enable_timer...