create DataFrame with time differences
For my scientific experiments I have a lot of data which are time-related. The absolute date here is irrelevant, what matters is the time since the start of the test. I also get results from different devices, with different sampling intervals and have to combine those. 
Now I do this by setting all experiments on a standard date, and adding the time difference with a timedelta. If I need the time since the start again I substract this standard date. This seems a bit unnecessary to me and complicates things, so  would it be possible to have a list of timedeltas or times as indices, not datetimes.

some example data
# File 1

"File Number";"D0";"D1";"E"
0;303,014862061;303,014862061;0
1;303,014862061;303,028381348;4,46159210696e-05
2;303,014862061;302,939239502;-0,000249567150604
3;303,014862061;302,947784424;-0,000221367474296
# File 2

Count;Filename_0;Filename_1;Time_0;Time_1;load;;;;Voltage_0;Voltage_1;Voltage_2;Voltage_3
0;G:/Limess data/Maarten/Sabic\PB-0_23_1-0000_0.tif;G:/Limess data/Maarten/Sabic\PB- \ 0_23_1-0000_1.tif;2610,926;2610,937;6,416;4,883;0,000;0,000;6,421;0,000;-0,049;0,024
1;G:/Limess data/Maarten/Sabic\PB-0_23_1-0001_0.tif;G:/Limess data/Maarten/Sabic\PB- \ 0_23_1-0001_1.tif;2805,331;2805,343;0,190;0,000;0,000;0,000;0,190;0,000;-0,088;-0,127
2;G:/Limess data/Maarten/Sabic\PB-0_23_1-0002_0.tif;G:/Limess data/Maarten/Sabic\PB- \ 0_23_1-0002_1.tif;2805,570;2805,570;0,190;4,883;0,000;0,000;0,195;0,000;-0,088;-0,127
3;G:/Limess data/Maarten/Sabic\PB-0_23_1-0003_0.tif;G:/Limess data/Maarten/Sabic\PB- \ 0_23_1-0003_1.tif;2805,849;2805,877;0,186;4,883;0,000;0,000;0,190;0,000;-0,088;-0,127
# File 3

Time;Extension;Load;Compressive strain (Extension);Compressive stress
"0,00000";"0,00000";"0,35976";"0,00000";"0,01799"
"0,10000";"0,00019";"-0,46161";"0,00001";"-0,02308"
"0,20000";"0,00063";"0,18237";"0,00003";"0,00912"
"0,30000";"0,00168";"0,42205";"0,00007";"0,02110"
"0,40000";"0,00532";"5,28095";"0,00022";"0,26405"
"0,50000";"0,00821";"9,91459";"0,00034";"0,49573"
"0,60000";"0,00973";"9,33031";"0,00040";"0,46652"
