Original version corrected from Arduino, which is an industry standard copy of the normal NTP function which has been around for decades. This library offers async NTP, which returns the seconds from Epoch (1970 and beyond) in 2 variations for use with Watchy watch face code.
Begin(String NTPServer): Start a call to the NTPServer asking for the current Epoch time (UTC starting at 1970).
bool Query(): Returns true if the NTPServer's response has come in, this can be done in a loop.
End(): Stop SmallNTP from continuing in the background, do this if you get a Query() result of true or false.
time_t MakeTime(tmElements_t TM) A TimeLib.h & time.h compliant version of makeTime().
BreakTime(time_t &T, tmElements_t &TM) TimeLib.h & time.h compliant version of breakTime().
Four variables that are filled when Query() returns true:
time_t Results: has the results of the NTPServer response in time_t format, ready for use with localtime.
tmElements_t tmResults has the results from above in a format to use in either WatchyRTC or SmallRTC (GuruSR).
time_t Results1900: has the results of the NTPServer response in time_t format since 1900, ready for use with localtime.
tmElements_t tmResults1900 has the results from above in a format to use in either WatchyRTC or SmallRTC (GuruSR).
None of the four above variables survive a Deep Sleep, do not rely on them after a Deep Sleep.
How to use in your Watchy.
#include <SmallNTP.h>
...
SmallNTP sNTP; // Declare NTP object
Start the NTP process with Begin, then use Query in a loop for say 5 seconds to get the response or a timeout (your 5 seconds pass), if the Query is true, store the results from tmResults into RTC.set. For TimeZone correction I would recommend including SmallRTC and Olson2POSIX for a complete suite of functionality.
IE:
sNTP.Begin("pool.ntp.org");
int s = 0;
bool b = false;
while (!b && s < 100){
s++;
delay(50);
b = sNTP.Query();
}
if (b) RTC.set(sNTP.tmResults);
sNTP.End();