Time Conduit

Upon casting this spell, a shimmering, golden portal appears somewhere within 30 feet of the caster (though the caster has no control over where the portal appears). This golden disk appears upon the fourth round of casting, and it grows, expanding as if it were an opening eye until it reaches its maximum diameter. At the completion of the casting, the 10‐foot circular opening goes translucent as the golden light of its edges dissipates back inside its radius, making the portal suddenly seem to lead into a long tunnel filled with electric silver‐and‐blue flashes of light. Creatures that gaze into the opening for more than one round see quick glimpses of their pasts cascading along the walls of the tunnel, but no memories or revisited scenes cause any damage.

The portal remains for one round per level of the caster or until the caster enters the conduit, whichever occurs first.
During the casting, the caster names the age and year that the time conduit is to transport those who enter it.

There is never a way to determine the precise physical destination when using a time conduit spell. The only thing for certain is that the time travelers appear somewhere in the lands of the culture they seek. Depending on the concentration and focus of the caster, a time conduit generally lands its travelers within 100 miles of areas claimed by the chosen culture. If no culture is specifically sought, the travelers would exit the time conduit at the chosen time, but they could arrive anywhere within 500 miles of their physical location where the time conduit is cast.

Time travelers always arrive during the early hours of the first day of the new year, and they always return to their own original times during the final night of the year. Nothing can prevent a time traveler from being drawn back into the time conduit at the close of the year, not even spells that negate magic or shield against its effects. Creatures return to their own time 30 days after they entered the time conduit originally, though they have physically aged one year due to their time trip.

Time travelers also cannot physically exist in two places at once within the same timeline. Therefore once a creature has traveled back to a particular year he can never visit that particular year again. Any attempt to do so fails utterly, and the caster (or a traveler who has visited the conduit’s exiting point in time) is hurled 1d100 years and 10d100 miles to a random time and place in the past. 

There are a wide range of side effects to travel by time conduits that were far more surprising and disturbing to time‐travelers; these are noted below within the spell itself. Creatures entering the time conduit are immediately stripped of all magical items and memorized spells and psionics, though the psionics return at the standard rate of restoration. Spell books and scrolls remain intact in function; though they are slightly altered (see below). Items that do not yet exist among the culture specified within the casting or among the race to which the caster belongs (if a culture was not chosen by the caster by the use of its calendar) also disappear; for example, plate armor disappears from all folk but dwarves and elves, while arquebuses vanish from all folks’ grasp. 
All appropriated items are shunted into sub dimensional pockets within the time conduit itself, and all of these are returned to the proper time travelers upon the voyage home. This return trip likewise strips travelers of items they collect during their stay in the past and stores them within the time conduit; where these items go after the conclusion of the spell is unknown, though many wizards believe any time‐lost items simply drift into the Ethereal Plane. Spells that do not exist for the caster’s race in the now‐current year appear as blank pages in a caster’s spell book. Scrolls for spells or effects that do not yet exist are also blank. These blank pages are restored to normal upon reaching the caster’s own time or a point in time where the spells exist for the caster’s race.

Credit to Sylrae on enworld. org /threads/forgotten-realms-time-travel-updated-to-3e.212974/