Arduino Uno Compatible Boards

there many Arduino Uno compatible boards but i am confused about it. the Uno now uses an ATmega16U2, 32U4 etc.

do i need to change my code if i use this board? code uses interrupt and timers., is there any that i need to change?

The UNO uses ATmega328P pretty long time. ATmega16U2 on the UNO board is in the role of USB/serial transceiver. Some other, compatible, boards can use FT232 chip or CH340... at this place, but it has nothing with main MCU ATmega328P. Simple answer is NO.