Genesis is silent on the concept of time (Refer). Also the total time from the time God started creation till date is just approx 5000 Years. This is almost nothing. God was said to have created Sun and moon on 3rd dauy only. So wahat does the first day and second day mean.
In his Book “Brief history of Time by” Stephen Hawking quotes a incident in the beginning of the Book that during a seminar a father was describing the genesis and a lady got up and asked “what was god doing before he created this universe”. The witty father dodged the question by “saying he was creating hell for people asking such questions”. In the End Hawking explains that fourth dimension time was also created only at the time of creation of universe. So what God did before has no meaning as before itself is dependent on time
Now let us peep into Manusmriti and see what it says.
1.24 कालं कलविभिश् च नक्षत्राणि हां स् तथा | सरितः सागरान् शौलान् सामानि विषमानि च ||
1.24. Time and the divisions of time, the lunar mansions and the planets, the rivers, the oceans, the mountains, plains, and uneven ground.
Thus Time creation is mentioned in Manusmriti and also its divisions were clearly defined
1.64 निमेषा दश च अष्टौ च काष्टा त्रिंशत् तु ताः कला | त्रिंशत् कला मुहूर्तः स्याद अहोरात्रं तु तावतः ||
1.64. Eighteen nimeshas (twinklings of the eye, are one kashtha), thirty kashthas one kala, thirty kalas one muhurta, and as many (muhurtas) one day and night.
Creation of universe and time elapsed is described in following slokas.
1.66 A months is (full moon to full moon) day for manes 1.67 A year is day for Gods. 1.69 But for Brahman (the Creator of Universe) 4000 years of God ( In effect it is our 4000 X 365 Years = 1,460,000 Years) is one kritayuga. 1.71And thus 12000 years of gods is one day for Brahman ( 1,460,000 X 3 = 4,380,000 ). 
This is supposed to be the total period of creation. Yes this also falls short of scientific period of Earths creation till Date. Scientific calculation (of Earth) is 4.6 Billion years till Date. Not Million as in Manusmriti. Human kind is just 4.6 million years. This seems to tally with the 4.38 Million Years. Well give or take there can be some more errors in interpretations and corrected.
But 1 conclusion is clear Manusmriti has a better concept on time. This is to be expected because 2000 years back itself Horoscope was a scientific subject and calculation of Eclipses were pretty accurate.
Understanding Ramayana 