[Fix] Session Duration trajectory timezone(UTC) & Today filter order

[bezhanSalleh]

fixes #67

[what-the-diff]

PR Summary

• Improved Timestamp Generation: Altered the method of creating timestamps in our code. This will ensure accuracy in time management operations which should improve our system's timing functions.
• Simplified Sign Calculation Process: Replaced a complex process of calculating the 'sign' of a value (whether it's negative or positive) with a new method. This presents the same outcome in a more understandable manner, making the code easier to maintain.
• New Method for Sign Determination: Introduced a new function specifically to determine the sign of a number. This focuses on the result of its calculation, improving the adaptability of the code.
• Optimized Session Duration Process: Modified the method of assigning session durations to better reflect their actual span. This change should lead to more accurate data about individual session lengths.