typedef std::chrono::high_resolution_clock::time_point TP;

double _estimatedGrowFinish = o.getPlantTimeEstimatedGrowingStopped(); // `14903312`

TP _now = std::chrono::high_resolution_clock::now();

TP _end = ??

std::chrono::high_resolution_clock::now() + std::chrono::seconds(20)

TEXT as ISO8601 strings ("YYYY-MM-DD HH:MM:SS.SSS").

REAL as Julian day numbers, the number of days since noon in Greenwich on November 24, 4714 B.C. according to the proleptic Gregorian calendar.

INTEGER as Unix Time, the number of seconds since 1970-01-01 00:00:00 UTC.

double const JulianEpoch = days_from_civil(-4714+1, 11, 24) - 0.5;

double estimatedGrowFinishJulian = getPlantTimeEstimatedGrowingStopped(); // `14903312`

double estimatedGrowFinishCivil = estimatedGrowFinishJulian + JulianEpoch;

using days = std::chrono::duration
    <
        double,
        std::ratio_multiply<std::chrono::hours::period, std::ratio<24>>
    >;

days estimatedGrowFinish(estimatedGrowFinishJulian + JulianEpoch);

using DTP = std::chrono::time_point
    <
        std::chrono::system_clock,
        days
    >;

DTP end(days(estimatedGrowFinishJulian + JulianEpoch));

std::cout << (end - now).count() << 'n';