can i pass variables of one ampscript to another, i want to set value for a variable in one ampscript and want to use the same variable in another ampscript.

Can we use sysmodstamp instead of lastmodifieddate in soql where clause

ex: select id from object where sysmodstamp > sampledate
currently we have in batch class is , select id from object where lastmodifieddate > sampledate 

we need to fetch large volumes from custom object and currently while fetching records using lastmodifieddate is getting timedout in batch apex, can i replace lastmodifiedate to sysmodstamp as it is an index field.