manage time with 'if ' bloc simulink

I created a function if with 'if block' simulink , with two condition if x = 1 then A else B but when X changed simulink does not have enough time to compute A then B or B then A ....

-i'm working in real time -I used the block 'MERGE' to combine the output how I can manage the time .. should i add ''MEMORY BLOCK''? help please

[Kaustubha Govind]

zikouoo: Sorry, your question is very confusing. Could you explain a little more what you mean by "but when X changed simulink does not have enough time to compute A then B or B then A" - do you mean there is an overrun in the generated code?