Issue Programming 0.96" i2c Oled and RTC Board with and ATtiny85?

When I turn on the ATtiny, the OLED just blinks rapidly 10: 10: 10 instead of the time. Both the OLED and the RTC have been confirmed working on an Uno, and the correct time has been set on the RTC. I have tried many different variations of this code, but i cant seem to get this to work. Any help is appreciated.

// necessary libraries
#include <TinyWireM.h>
#include <Tiny4kOLED.h>
#include <TinyRTClib.h>


RTC_DS1307 rtc;

//varibles used to store current hour, minute, second
int hours;
int minutes;
int secs;

//string used to display current time.
String timestr = "";

void setup () {

//initiates the oled.
  oled.begin();
  oled.clear();
  oled.on();

}

void loop () {
  DateTime now = rtc.now();

//clears, sets font, positions cursot to top left on OLED
  oled.clear();
  oled.setFont(FONT8X16);
  oled.setCursor(0, 0);

//puts current time in to the variables
  hours = int(now.hour(), DEC);
  minutes = int(now.minute(), DEC);
  secs = int(now.second(), DEC);

//formats the string used for displaying the time  
  timestr = String(hours)  + ": " + String(minutes) + ": " + String(secs);

//displays the time strimg
  oled.print(timestr);
  oled.switchFrame();

}

//varibles used to store current hour, minute, second
int hours;
int minutes;
int secs;

What part of the universe do you live in, where there are more than 255 seconds in a minute, more than 255 minutes in an hour, and more than 255 hours in a day?

//string used to display current time.
String timestr = "";

That was as far as I got. You appear to have memory issues, but persist in pissing it away uselessly.