OB35 is a cyclic interrupt OB (like all other OBs in th erange OB30-OB38), this means it is called every... ms (user adaptable time). What I think you want to do is called an interrupt and this feature is also available but in OB40 - OB47. These OBs can be called on a hardware event (e.g. the push of a button). Further you have the time of day OBs (OB10 - OB17), that are called on a user defined time and date (e.g. every monday morning at 8 a.m.) and the time delay OBs (OB20-OB23) that are called a user defined time after a call to SFC32 (SRT_DINT). This can also be used to create a software interrupt if the delay time is set to 0. In howfar these OBs are available in PLC sim I don't know, PLC Sim is only a simulated environment, not the real thing. But you see that what you propose already exists in some form or other (and most of these functions already existed in S5).
